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 $117.87   6.610%   $125.6612   $125.66   $125.65   $125.70  
  Purchase #2 $56.68   7.148%   $60.7315   $60.73   $60.75   $60.70  
  Purchase #3 $5.90   9.537%   $6.4627   $6.46   $6.45   $6.50  
  Purchase #4 $10.29   13.207%   $11.649   $11.65   $11.65   $11.60  
  Purchase #5 $25.69   5.241%   $27.0364   $27.04   $27.05   $27.00  
  Purchase #6 $91.63   12.655%   $103.2258   $103.23   $103.25   $103.20  
  Purchase #7 $206.58   5.532%   $218.008   $218.01   $218.00   $218.00  
  7 purchase totals = $514.64       $552.7746   $552.78   $552.80   $552.70