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 $169.82   13.619%   $192.9478   $192.95   $192.95   $192.90  
  Purchase #2 $76.44   11.613%   $85.317   $85.32   $85.30   $85.30  
  Purchase #3 $39.50   6.669%   $42.1343   $42.13   $42.15   $42.10  
  Purchase #4 $62.37   13.717%   $70.9253   $70.93   $70.95   $70.90  
  Purchase #5 $206.75   13.691%   $235.0561   $235.06   $235.05   $235.10  
  Purchase #6 $237.87   9.586%   $260.6722   $260.67   $260.65   $260.70  
  Purchase #7 $30.94   4.621%   $32.3697   $32.37   $32.35   $32.40  
  7 purchase totals = $823.69       $919.4224   $919.43   $919.40   $919.40