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 $60.42   13.242%   $68.4208   $68.42   $68.40   $68.40  
  Purchase #2 $189.74   4.176%   $197.6635   $197.66   $197.65   $197.70  
  Purchase #3 $245.39   3.752%   $254.597   $254.60   $254.60   $254.60  
  Purchase #4 $164.55   12.171%   $184.5774   $184.58   $184.60   $184.60  
  Purchase #5 $193.38   7.176%   $207.2569   $207.26   $207.25   $207.30  
  Purchase #6 $15.30   11.240%   $17.0197   $17.02   $17.00   $17.00  
  Purchase #7 $212.82   13.472%   $241.4911   $241.49   $241.50   $241.50  
  7 purchase totals = $1,081.60       $1,171.0264   $1,171.03   $1,171.00   $1,171.10