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 $28.91   11.310%   $32.1797   $32.18   $32.20   $32.20  
  Purchase #2 $62.91   12.665%   $70.8776   $70.88   $70.90   $70.90  
  Purchase #3 $117.56   7.203%   $126.0278   $126.03   $126.05   $126.00  
  Purchase #4 $151.72   9.282%   $165.8027   $165.80   $165.80   $165.80  
  Purchase #5 $188.60   3.361%   $194.9388   $194.94   $194.95   $194.90  
  Purchase #6 $200.85   4.157%   $209.1993   $209.20   $209.20   $209.20  
  Purchase #7 $150.42   6.148%   $159.6678   $159.67   $159.65   $159.70  
  7 purchase totals = $900.97       $958.6937   $958.70   $958.75   $958.70