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 $54.91   8.530%   $59.5938   $59.59   $59.60   $59.60  
  Purchase #2 $201.39   9.153%   $219.8232   $219.82   $219.80   $219.80  
  Purchase #3 $214.51   6.534%   $228.5261   $228.53   $228.55   $228.50  
  Purchase #4 $45.81   4.155%   $47.7134   $47.71   $47.70   $47.70  
  Purchase #5 $126.45   9.463%   $138.416   $138.42   $138.40   $138.40  
  Purchase #6 $61.73   11.286%   $68.6968   $68.70   $68.70   $68.70  
  Purchase #7 $250.38   9.508%   $274.1861   $274.19   $274.20   $274.20  
  7 purchase totals = $955.18       $1,036.9554   $1,036.96   $1,036.95   $1,036.90