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 $55.42   9.571%   $60.7242   $60.72   $60.70   $60.70  
  Purchase #2 $201.77   13.347%   $228.7002   $228.70   $228.70   $228.70  
  Purchase #3 $86.84   8.515%   $94.2344   $94.23   $94.25   $94.20  
  Purchase #4 $157.62   13.419%   $178.771   $178.77   $178.75   $178.80  
  Purchase #5 $82.60   11.270%   $91.909   $91.91   $91.90   $91.90  
  Purchase #6 $93.61   7.135%   $100.2891   $100.29   $100.30   $100.30  
  Purchase #7 $55.59   8.491%   $60.3101   $60.31   $60.30   $60.30  
  7 purchase totals = $733.45       $814.9380   $814.93   $814.90   $814.90