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 $50.85   7.466%   $54.6465   $54.65   $54.65   $54.60  
  Purchase #2 $46.30   9.474%   $50.6865   $50.69   $50.70   $50.70  
  Purchase #3 $145.92   5.187%   $153.4889   $153.49   $153.50   $153.50  
  Purchase #4 $170.34   5.749%   $180.1328   $180.13   $180.15   $180.10  
  Purchase #5 $204.82   9.687%   $224.6609   $224.66   $224.65   $224.70  
  Purchase #6 $34.94   4.164%   $36.3949   $36.39   $36.40   $36.40  
  Purchase #7 $31.42   5.149%   $33.0378   $33.04   $33.05   $33.00  
  7 purchase totals = $684.59       $733.0483   $733.05   $733.10   $733.00