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 $20.54   7.713%   $22.1243   $22.12   $22.10   $22.10  
  Purchase #2 $43.25   13.548%   $49.1095   $49.11   $49.10   $49.10  
  Purchase #3 $184.69   5.200%   $194.2939   $194.29   $194.30   $194.30  
  Purchase #4 $108.75   12.261%   $122.0838   $122.08   $122.10   $122.10  
  Purchase #5 $17.69   5.683%   $18.6953   $18.70   $18.70   $18.70  
  Purchase #6 $22.69   7.133%   $24.3085   $24.31   $24.30   $24.30  
  Purchase #7 $119.66   6.612%   $127.5719   $127.57   $127.55   $127.60  
  7 purchase totals = $517.27       $558.1872   $558.18   $558.15   $558.20