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 $174.52   11.317%   $194.2704   $194.27   $194.25   $194.30  
  Purchase #2 $27.97   12.118%   $31.3594   $31.36   $31.35   $31.40  
  Purchase #3 $119.85   8.453%   $129.9809   $129.98   $130.00   $130.00  
  Purchase #4 $209.89   11.611%   $234.2603   $234.26   $234.25   $234.30  
  Purchase #5 $217.29   8.813%   $236.4398   $236.44   $236.45   $236.40  
  Purchase #6 $234.68   3.245%   $242.2954   $242.30   $242.30   $242.30  
  Purchase #7 $88.28   12.519%   $99.3318   $99.33   $99.35   $99.30  
  7 purchase totals = $1,072.48       $1,167.9380   $1,167.94   $1,167.95   $1,168.00