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 $131.26   13.514%   $148.9985   $149.00   $149.00   $149.00  
  Purchase #2 $249.54   7.266%   $267.6716   $267.67   $267.65   $267.70  
  Purchase #3 $53.33   9.601%   $58.4502   $58.45   $58.45   $58.50  
  Purchase #4 $123.95   6.731%   $132.2931   $132.29   $132.30   $132.30  
  Purchase #5 $90.39   5.847%   $95.6751   $95.68   $95.70   $95.70  
  Purchase #6 $70.46   13.250%   $79.796   $79.80   $79.80   $79.80  
  Purchase #7 $71.29   6.854%   $76.1762   $76.18   $76.20   $76.20  
  7 purchase totals = $790.22       $859.0607   $859.07   $859.10   $859.20