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 $180.77   11.607%   $201.752   $201.75   $201.75   $201.80  
  Purchase #2 $100.66   13.265%   $114.0125   $114.01   $114.00   $114.00  
  Purchase #3 $168.87   12.322%   $189.6782   $189.68   $189.70   $189.70  
  Purchase #4 $170.33   7.274%   $182.7198   $182.72   $182.70   $182.70  
  Purchase #5 $221.86   9.645%   $243.2584   $243.26   $243.25   $243.30  
  Purchase #6 $224.82   8.482%   $243.8892   $243.89   $243.90   $243.90  
  Purchase #7 $63.65   13.563%   $72.2828   $72.28   $72.30   $72.30  
  7 purchase totals = $1,130.96       $1,247.5929   $1,247.59   $1,247.60   $1,247.70