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 $58.69   8.421%   $63.6323   $63.63   $63.65   $63.60  
  Purchase #2 $179.55   13.353%   $203.5253   $203.53   $203.55   $203.50  
  Purchase #3 $62.44   5.177%   $65.6725   $65.67   $65.65   $65.70  
  Purchase #4 $192.36   8.367%   $208.4548   $208.45   $208.45   $208.50  
  Purchase #5 $86.62   12.842%   $97.7437   $97.74   $97.75   $97.70  
  Purchase #6 $143.92   8.294%   $155.8567   $155.86   $155.85   $155.90  
  Purchase #7 $78.26   9.112%   $85.3911   $85.39   $85.40   $85.40  
  7 purchase totals = $801.84       $880.2764   $880.27   $880.30   $880.30