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 $90.85   4.277%   $94.7357   $94.74   $94.75   $94.70  
  Purchase #2 $191.27   10.432%   $211.2233   $211.22   $211.20   $211.20  
  Purchase #3 $26.30   3.836%   $27.3089   $27.31   $27.30   $27.30  
  Purchase #4 $72.44   3.211%   $74.766   $74.77   $74.75   $74.80  
  Purchase #5 $87.81   11.735%   $98.1145   $98.11   $98.10   $98.10  
  Purchase #6 $139.27   4.824%   $145.9884   $145.99   $146.00   $146.00  
  Purchase #7 $125.62   4.474%   $131.2402   $131.24   $131.25   $131.20  
  7 purchase totals = $733.56       $783.3770   $783.38   $783.35   $783.30