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 $92.44   6.164%   $98.138   $98.14   $98.15   $98.10  
  Purchase #2 $224.67   10.679%   $248.6625   $248.66   $248.65   $248.70  
  Purchase #3 $242.99   9.660%   $266.4628   $266.46   $266.45   $266.50  
  Purchase #4 $200.84   13.632%   $228.2185   $228.22   $228.20   $228.20  
  Purchase #5 $221.31   7.448%   $237.7932   $237.79   $237.80   $237.80  
  Purchase #6 $135.30   11.192%   $150.4428   $150.44   $150.45   $150.40  
  Purchase #7 $50.43   8.671%   $54.8028   $54.80   $54.80   $54.80  
  7 purchase totals = $1,167.98       $1,284.5206   $1,284.51   $1,284.50   $1,284.50