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 $241.37   3.617%   $250.1004   $250.10   $250.10   $250.10  
  Purchase #2 $28.55   10.452%   $31.534   $31.53   $31.55   $31.50  
  Purchase #3 $180.29   7.640%   $194.0642   $194.06   $194.05   $194.10  
  Purchase #4 $215.39   7.541%   $231.6326   $231.63   $231.65   $231.60  
  Purchase #5 $86.27   8.530%   $93.6288   $93.63   $93.65   $93.60  
  Purchase #6 $30.72   9.205%   $33.5478   $33.55   $33.55   $33.50  
  Purchase #7 $36.84   8.593%   $40.0057   $40.01   $40.00   $40.00  
  7 purchase totals = $819.43       $874.5135   $874.51   $874.55   $874.40