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 $88.93   7.534%   $95.63   $95.63   $95.65   $95.60  
  Purchase #2 $99.46   7.262%   $106.6828   $106.68   $106.70   $106.70  
  Purchase #3 $65.51   5.417%   $69.0587   $69.06   $69.05   $69.10  
  Purchase #4 $195.89   13.307%   $221.9571   $221.96   $221.95   $222.00  
  Purchase #5 $32.90   10.857%   $36.472   $36.47   $36.45   $36.50  
  Purchase #6 $66.81   11.807%   $74.6983   $74.70   $74.70   $74.70  
  Purchase #7 $128.56   13.291%   $145.6469   $145.65   $145.65   $145.60  
  7 purchase totals = $678.06       $750.1458   $750.15   $750.15   $750.20