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 $105.94   11.661%   $118.2937   $118.29   $118.30   $118.30  
  Purchase #2 $159.77   9.495%   $174.9402   $174.94   $174.95   $174.90  
  Purchase #3 $220.58   13.161%   $249.6105   $249.61   $249.60   $249.60  
  Purchase #4 $23.53   10.537%   $26.0094   $26.01   $26.00   $26.00  
  Purchase #5 $200.94   6.811%   $214.626   $214.63   $214.65   $214.60  
  Purchase #6 $231.34   6.185%   $245.6484   $245.65   $245.65   $245.60  
  Purchase #7 $228.46   7.581%   $245.7796   $245.78   $245.80   $245.80  
  7 purchase totals = $1,170.56       $1,274.9078   $1,274.91   $1,274.95   $1,274.80