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 $235.35   13.608%   $267.3764   $267.38   $267.40   $267.40  
  Purchase #2 $156.90   11.567%   $175.0486   $175.05   $175.05   $175.00  
  Purchase #3 $78.44   9.626%   $85.9906   $85.99   $86.00   $86.00  
  Purchase #4 $128.51   13.648%   $146.049   $146.05   $146.05   $146.00  
  Purchase #5 $41.98   5.273%   $44.1936   $44.19   $44.20   $44.20  
  Purchase #6 $87.83   12.208%   $98.5523   $98.55   $98.55   $98.60  
  Purchase #7 $184.87   12.356%   $207.7125   $207.71   $207.70   $207.70  
  7 purchase totals = $913.88       $1,024.9230   $1,024.92   $1,024.95   $1,024.90