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 $90.97   4.778%   $95.3165   $95.32   $95.30   $95.30  
  Purchase #2 $70.43   7.535%   $75.7369   $75.74   $75.75   $75.70  
  Purchase #3 $107.46   5.123%   $112.9652   $112.97   $112.95   $113.00  
  Purchase #4 $41.28   11.483%   $46.0202   $46.02   $46.00   $46.00  
  Purchase #5 $166.95   12.561%   $187.9206   $187.92   $187.90   $187.90  
  Purchase #6 $223.62   9.397%   $244.6336   $244.63   $244.65   $244.60  
  Purchase #7 $171.47   5.855%   $181.5096   $181.51   $181.50   $181.50  
  7 purchase totals = $872.18       $944.1026   $944.11   $944.05   $944.00