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 $63.47   8.613%   $68.9367   $68.94   $68.95   $68.90  
  Purchase #2 $53.35   4.724%   $55.8703   $55.87   $55.85   $55.90  
  Purchase #3 $172.59   4.299%   $180.0096   $180.01   $180.00   $180.00  
  Purchase #4 $222.55   5.504%   $234.7992   $234.80   $234.80   $234.80  
  Purchase #5 $106.88   3.794%   $110.935   $110.94   $110.95   $110.90  
  Purchase #6 $104.89   5.817%   $110.9915   $110.99   $111.00   $111.00  
  Purchase #7 $232.29   10.747%   $257.2542   $257.25   $257.25   $257.30  
  7 purchase totals = $956.02       $1,018.7965   $1,018.80   $1,018.80   $1,018.80