Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $186.76   8.440%   $202.5225   $202.52   $202.50   $202.50  
  Purchase #2 $181.77   6.541%   $193.6596   $193.66   $193.65   $193.70  
  Purchase #3 $165.78   11.761%   $185.2774   $185.28   $185.30   $185.30  
  Purchase #4 $183.53   11.740%   $205.0764   $205.08   $205.10   $205.10  
  Purchase #5 $218.35   12.359%   $245.3359   $245.34   $245.35   $245.30  
  Purchase #6 $119.25   5.261%   $125.5237   $125.52   $125.50   $125.50  
  Purchase #7 $68.96   6.244%   $73.2659   $73.27   $73.25   $73.30  
  7 purchase totals = $1,124.40       $1,230.6614   $1,230.67   $1,230.65   $1,230.70