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 $59.60   6.606%   $63.5372   $63.54   $63.55   $63.50  
  Purchase #2 $41.49   5.159%   $43.6305   $43.63   $43.65   $43.60  
  Purchase #3 $104.87   10.236%   $115.6045   $115.60   $115.60   $115.60  
  Purchase #4 $171.42   10.391%   $189.2323   $189.23   $189.25   $189.20  
  Purchase #5 $199.52   5.414%   $210.322   $210.32   $210.30   $210.30  
  Purchase #6 $65.46   12.642%   $73.7355   $73.74   $73.75   $73.70  
  Purchase #7 $220.63   3.426%   $228.1888   $228.19   $228.20   $228.20  
  7 purchase totals = $862.99       $924.2508   $924.25   $924.30   $924.10