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 $211.90   13.870%   $241.2905   $241.29   $241.30   $241.30  
  Purchase #2 $250.36   9.354%   $273.7787   $273.78   $273.80   $273.80  
  Purchase #3 $111.75   9.762%   $122.659   $122.66   $122.65   $122.70  
  Purchase #4 $114.37   12.480%   $128.6434   $128.64   $128.65   $128.60  
  Purchase #5 $140.37   6.123%   $148.9649   $148.96   $148.95   $149.00  
  Purchase #6 $79.80   5.276%   $84.0102   $84.01   $84.00   $84.00  
  Purchase #7 $65.63   13.177%   $74.2781   $74.28   $74.30   $74.30  
  7 purchase totals = $974.18       $1,073.6248   $1,073.62   $1,073.65   $1,073.70