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 $136.98   10.236%   $151.0013   $151.00   $151.00   $151.00  
  Purchase #2 $152.37   11.810%   $170.3649   $170.36   $170.35   $170.40  
  Purchase #3 $49.34   6.472%   $52.5333   $52.53   $52.55   $52.50  
  Purchase #4 $153.71   11.480%   $171.3559   $171.36   $171.35   $171.40  
  Purchase #5 $68.60   7.495%   $73.7416   $73.74   $73.75   $73.70  
  Purchase #6 $185.44   11.442%   $206.658   $206.66   $206.65   $206.70  
  Purchase #7 $106.86   11.485%   $119.1329   $119.13   $119.15   $119.10  
  7 purchase totals = $853.30       $944.7879   $944.78   $944.80   $944.80