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 $201.38   6.759%   $214.9913   $214.99   $215.00   $215.00  
  Purchase #2 $151.77   8.842%   $165.1895   $165.19   $165.20   $165.20  
  Purchase #3 $126.64   13.269%   $143.4439   $143.44   $143.45   $143.40  
  Purchase #4 $173.45   12.194%   $194.6005   $194.60   $194.60   $194.60  
  Purchase #5 $172.49   6.182%   $183.1533   $183.15   $183.15   $183.20  
  Purchase #6 $73.56   4.573%   $76.9239   $76.92   $76.90   $76.90  
  Purchase #7 $46.74   12.300%   $52.489   $52.49   $52.50   $52.50  
  7 purchase totals = $946.03       $1,030.7914   $1,030.78   $1,030.80   $1,030.80