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 $146.26   4.708%   $153.1459   $153.15   $153.15   $153.10  
  Purchase #2 $33.85   4.309%   $35.3086   $35.31   $35.30   $35.30  
  Purchase #3 $218.63   11.779%   $244.3824   $244.38   $244.40   $244.40  
  Purchase #4 $176.74   4.232%   $184.2196   $184.22   $184.20   $184.20  
  Purchase #5 $101.52   7.796%   $109.4345   $109.43   $109.45   $109.40  
  Purchase #6 $149.86   11.546%   $167.1628   $167.16   $167.15   $167.20  
  Purchase #7 $151.34   11.692%   $169.0347   $169.03   $169.05   $169.00  
  7 purchase totals = $978.20       $1,062.6885   $1,062.68   $1,062.70   $1,062.60