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 $195.62   9.397%   $214.0024   $214.00   $214.00   $214.00  
  Purchase #2 $64.53   9.172%   $70.4487   $70.45   $70.45   $70.40  
  Purchase #3 $118.31   13.500%   $134.2819   $134.28   $134.30   $134.30  
  Purchase #4 $240.75   9.646%   $263.9727   $263.97   $263.95   $264.00  
  Purchase #5 $162.37   3.607%   $168.2267   $168.23   $168.25   $168.20  
  Purchase #6 $67.70   6.679%   $72.2217   $72.22   $72.20   $72.20  
  Purchase #7 $83.32   10.626%   $92.1736   $92.17   $92.15   $92.20  
  7 purchase totals = $932.60       $1,015.3277   $1,015.32   $1,015.30   $1,015.30