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 $191.68   11.224%   $213.1942   $213.19   $213.20   $213.20  
  Purchase #2 $179.75   6.683%   $191.7627   $191.76   $191.75   $191.80  
  Purchase #3 $72.65   4.874%   $76.191   $76.19   $76.20   $76.20  
  Purchase #4 $237.35   4.317%   $247.5964   $247.60   $247.60   $247.60  
  Purchase #5 $181.42   11.293%   $201.9078   $201.91   $201.90   $201.90  
  Purchase #6 $59.27   6.588%   $63.1747   $63.17   $63.15   $63.20  
  Purchase #7 $120.83   4.594%   $126.3809   $126.38   $126.40   $126.40  
  7 purchase totals = $1,042.95       $1,120.2077   $1,120.20   $1,120.20   $1,120.30