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 $154.48   10.496%   $170.6942   $170.69   $170.70   $170.70  
  Purchase #2 $32.33   6.124%   $34.3099   $34.31   $34.30   $34.30  
  Purchase #3 $88.34   11.706%   $98.6811   $98.68   $98.70   $98.70  
  Purchase #4 $113.33   7.182%   $121.4694   $121.47   $121.45   $121.50  
  Purchase #5 $236.96   12.801%   $267.2932   $267.29   $267.30   $267.30  
  Purchase #6 $151.48   10.391%   $167.2203   $167.22   $167.20   $167.20  
  Purchase #7 $101.27   5.577%   $106.9178   $106.92   $106.90   $106.90  
  7 purchase totals = $878.19       $966.5859   $966.58   $966.55   $966.60