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 $88.29   11.648%   $98.574   $98.57   $98.55   $98.60  
  Purchase #2 $65.62   13.423%   $74.4282   $74.43   $74.45   $74.40  
  Purchase #3 $60.87   4.701%   $63.7315   $63.73   $63.75   $63.70  
  Purchase #4 $37.41   5.546%   $39.4848   $39.48   $39.50   $39.50  
  Purchase #5 $92.26   5.559%   $97.3887   $97.39   $97.40   $97.40  
  Purchase #6 $107.43   13.645%   $122.0888   $122.09   $122.10   $122.10  
  Purchase #7 $239.41   7.275%   $256.8271   $256.83   $256.85   $256.80  
  7 purchase totals = $691.29       $752.5231   $752.52   $752.60   $752.50