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 $239.83   10.213%   $264.3238   $264.32   $264.30   $264.30  
  Purchase #2 $143.43   6.434%   $152.6583   $152.66   $152.65   $152.70  
  Purchase #3 $119.29   6.188%   $126.6717   $126.67   $126.65   $126.70  
  Purchase #4 $156.28   3.803%   $162.2233   $162.22   $162.20   $162.20  
  Purchase #5 $205.59   7.578%   $221.1696   $221.17   $221.15   $221.20  
  Purchase #6 $43.59   6.566%   $46.4521   $46.45   $46.45   $46.50  
  Purchase #7 $210.27   11.544%   $234.5436   $234.54   $234.55   $234.50  
  7 purchase totals = $1,118.28       $1,208.0424   $1,208.03   $1,207.95   $1,208.10