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 $163.98   12.528%   $184.5234   $184.52   $184.50   $184.50  
  Purchase #2 $188.61   13.361%   $213.8102   $213.81   $213.80   $213.80  
  Purchase #3 $182.75   12.551%   $205.687   $205.69   $205.70   $205.70  
  Purchase #4 $219.49   8.608%   $238.3837   $238.38   $238.40   $238.40  
  Purchase #5 $215.30   4.477%   $224.939   $224.94   $224.95   $224.90  
  Purchase #6 $159.46   5.183%   $167.7248   $167.72   $167.70   $167.70  
  Purchase #7 $189.75   3.824%   $197.006   $197.01   $197.00   $197.00  
  7 purchase totals = $1,319.34       $1,432.0741   $1,432.07   $1,432.05   $1,432.00