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 $58.57   6.424%   $62.3325   $62.33   $62.35   $62.30  
  Purchase #2 $95.27   8.423%   $103.2946   $103.29   $103.30   $103.30  
  Purchase #3 $212.57   12.472%   $239.0817   $239.08   $239.10   $239.10  
  Purchase #4 $58.86   7.664%   $63.371   $63.37   $63.35   $63.40  
  Purchase #5 $22.91   7.543%   $24.6381   $24.64   $24.65   $24.60  
  Purchase #6 $219.70   12.549%   $247.2702   $247.27   $247.25   $247.30  
  Purchase #7 $117.94   9.510%   $129.1561   $129.16   $129.15   $129.20  
  7 purchase totals = $785.82       $869.1442   $869.14   $869.15   $869.20