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 $76.66   9.251%   $83.7518   $83.75   $83.75   $83.80  
  Purchase #2 $140.58   11.440%   $156.6624   $156.66   $156.65   $156.70  
  Purchase #3 $35.65   10.449%   $39.3751   $39.38   $39.40   $39.40  
  Purchase #4 $191.87   5.748%   $202.8987   $202.90   $202.90   $202.90  
  Purchase #5 $197.68   3.762%   $205.1167   $205.12   $205.10   $205.10  
  Purchase #6 $224.28   3.674%   $232.52   $232.52   $232.50   $232.50  
  Purchase #7 $57.95   9.657%   $63.5462   $63.55   $63.55   $63.50  
  7 purchase totals = $924.67       $983.8709   $983.88   $983.85   $983.90