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 $173.30   9.646%   $190.0165   $190.02   $190.00   $190.00  
  Purchase #2 $83.49   9.629%   $91.5293   $91.53   $91.55   $91.50  
  Purchase #3 $87.28   8.547%   $94.7398   $94.74   $94.75   $94.70  
  Purchase #4 $195.66   6.126%   $207.6461   $207.65   $207.65   $207.60  
  Purchase #5 $144.27   10.183%   $158.961   $158.96   $158.95   $159.00  
  Purchase #6 $173.76   12.465%   $195.4192   $195.42   $195.40   $195.40  
  Purchase #7 $175.35   10.732%   $194.1686   $194.17   $194.15   $194.20  
  7 purchase totals = $1,033.11       $1,132.4805   $1,132.49   $1,132.45   $1,132.40