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 $83.43   7.805%   $89.9417   $89.94   $89.95   $89.90  
  Purchase #2 $144.51   10.793%   $160.107   $160.11   $160.10   $160.10  
  Purchase #3 $95.80   12.204%   $107.4914   $107.49   $107.50   $107.50  
  Purchase #4 $171.40   3.218%   $176.9157   $176.92   $176.90   $176.90  
  Purchase #5 $25.93   4.857%   $27.1894   $27.19   $27.20   $27.20  
  Purchase #6 $100.40   9.586%   $110.0243   $110.02   $110.00   $110.00  
  Purchase #7 $14.78   7.341%   $15.865   $15.87   $15.85   $15.90  
  7 purchase totals = $636.25       $687.5345   $687.54   $687.50   $687.50