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 $188.53   13.510%   $214.0004   $214.00   $214.00   $214.00  
  Purchase #2 $249.35   5.378%   $262.76   $262.76   $262.75   $262.80  
  Purchase #3 $158.84   6.819%   $169.6713   $169.67   $169.65   $169.70  
  Purchase #4 $65.82   6.253%   $69.9357   $69.94   $69.95   $69.90  
  Purchase #5 $76.44   11.235%   $85.028   $85.03   $85.05   $85.00  
  Purchase #6 $112.41   9.252%   $122.8102   $122.81   $122.80   $122.80  
  Purchase #7 $140.88   6.255%   $149.692   $149.69   $149.70   $149.70  
  7 purchase totals = $992.27       $1,073.8976   $1,073.90   $1,073.90   $1,073.90