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 $84.29   13.779%   $95.9043   $95.90   $95.90   $95.90  
  Purchase #2 $242.68   10.737%   $268.7366   $268.74   $268.75   $268.70  
  Purchase #3 $10.81   9.663%   $11.8546   $11.85   $11.85   $11.90  
  Purchase #4 $93.58   6.460%   $99.6253   $99.63   $99.65   $99.60  
  Purchase #5 $163.68   11.173%   $181.968   $181.97   $181.95   $182.00  
  Purchase #6 $5.39   10.828%   $5.9736   $5.97   $5.95   $6.00  
  Purchase #7 $179.92   11.847%   $201.2351   $201.24   $201.25   $201.20  
  7 purchase totals = $780.35       $865.2975   $865.30   $865.30   $865.30