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 $105.69   13.711%   $120.1812   $120.18   $120.20   $120.20  
  Purchase #2 $42.95   6.739%   $45.8444   $45.84   $45.85   $45.80  
  Purchase #3 $26.74   9.171%   $29.1923   $29.19   $29.20   $29.20  
  Purchase #4 $208.78   11.561%   $232.9171   $232.92   $232.90   $232.90  
  Purchase #5 $95.98   9.441%   $105.0415   $105.04   $105.05   $105.00  
  Purchase #6 $230.48   8.864%   $250.9097   $250.91   $250.90   $250.90  
  Purchase #7 $160.92   13.738%   $183.0272   $183.03   $183.05   $183.00  
  7 purchase totals = $871.54       $967.1134   $967.11   $967.15   $967.00