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 $54.86   10.344%   $60.5347   $60.53   $60.55   $60.50  
  Purchase #2 $174.27   4.490%   $182.0947   $182.09   $182.10   $182.10  
  Purchase #3 $228.59   7.605%   $245.9743   $245.97   $245.95   $246.00  
  Purchase #4 $12.81   11.474%   $14.2798   $14.28   $14.30   $14.30  
  Purchase #5 $88.32   3.497%   $91.4086   $91.41   $91.40   $91.40  
  Purchase #6 $193.39   4.416%   $201.9301   $201.93   $201.95   $201.90  
  Purchase #7 $194.58   6.576%   $207.3756   $207.38   $207.40   $207.40  
  7 purchase totals = $946.82       $1,003.5978   $1,003.59   $1,003.65   $1,003.60