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 $21.27   3.796%   $22.0774   $22.08   $22.10   $22.10  
  Purchase #2 $209.25   8.729%   $227.5154   $227.52   $227.50   $227.50  
  Purchase #3 $51.70   9.193%   $56.4528   $56.45   $56.45   $56.50  
  Purchase #4 $178.96   8.870%   $194.8338   $194.83   $194.85   $194.80  
  Purchase #5 $118.91   9.391%   $130.0768   $130.08   $130.10   $130.10  
  Purchase #6 $243.30   6.700%   $259.6011   $259.60   $259.60   $259.60  
  Purchase #7 $182.76   9.575%   $200.2593   $200.26   $200.25   $200.30  
  7 purchase totals = $1,006.15       $1,090.8166   $1,090.82   $1,090.85   $1,090.90