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 $73.55   12.812%   $82.9732   $82.97   $82.95   $83.00  
  Purchase #2 $89.29   11.164%   $99.2583   $99.26   $99.25   $99.30  
  Purchase #3 $108.38   4.841%   $113.6267   $113.63   $113.65   $113.60  
  Purchase #4 $165.41   11.798%   $184.9251   $184.93   $184.95   $184.90  
  Purchase #5 $188.84   8.726%   $205.3182   $205.32   $205.30   $205.30  
  Purchase #6 $191.57   5.323%   $201.7673   $201.77   $201.75   $201.80  
  Purchase #7 $63.72   7.782%   $68.6787   $68.68   $68.70   $68.70  
  7 purchase totals = $880.76       $956.5475   $956.56   $956.55   $956.60