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 $245.34   11.674%   $273.981   $273.98   $274.00   $274.00  
  Purchase #2 $69.51   7.807%   $74.9366   $74.94   $74.95   $74.90  
  Purchase #3 $177.25   12.172%   $198.8249   $198.82   $198.80   $198.80  
  Purchase #4 $52.93   10.726%   $58.6073   $58.61   $58.60   $58.60  
  Purchase #5 $49.57   5.782%   $52.4361   $52.44   $52.45   $52.40  
  Purchase #6 $111.94   4.469%   $116.9426   $116.94   $116.95   $116.90  
  Purchase #7 $108.62   13.245%   $123.0067   $123.01   $123.00   $123.00  
  7 purchase totals = $815.16       $898.7352   $898.74   $898.75   $898.60