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 $184.98   11.564%   $206.3711   $206.37   $206.35   $206.40  
  Purchase #2 $174.79   11.366%   $194.6566   $194.66   $194.65   $194.70  
  Purchase #3 $190.95   13.539%   $216.8027   $216.80   $216.80   $216.80  
  Purchase #4 $102.92   3.466%   $106.4872   $106.49   $106.50   $106.50  
  Purchase #5 $43.38   11.303%   $48.2832   $48.28   $48.30   $48.30  
  Purchase #6 $142.83   11.484%   $159.2326   $159.23   $159.25   $159.20  
  Purchase #7 $84.59   5.800%   $89.4962   $89.50   $89.50   $89.50  
  7 purchase totals = $924.44       $1,021.3296   $1,021.33   $1,021.35   $1,021.40