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 $80.51   3.343%   $83.2014   $83.20   $83.20   $83.20  
  Purchase #2 $153.38   10.825%   $169.9834   $169.98   $170.00   $170.00  
  Purchase #3 $91.46   4.238%   $95.3361   $95.34   $95.35   $95.30  
  Purchase #4 $147.62   4.852%   $154.7825   $154.78   $154.80   $154.80  
  Purchase #5 $146.37   10.337%   $161.5003   $161.50   $161.50   $161.50  
  Purchase #6 $105.34   13.565%   $119.6294   $119.63   $119.65   $119.60  
  Purchase #7 $151.70   10.279%   $167.2932   $167.29   $167.30   $167.30  
  7 purchase totals = $876.38       $951.7263   $951.72   $951.80   $951.70