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 $162.82   12.710%   $183.5144   $183.51   $183.50   $183.50  
  Purchase #2 $209.81   10.236%   $231.2862   $231.29   $231.30   $231.30  
  Purchase #3 $110.73   13.758%   $125.9642   $125.96   $125.95   $126.00  
  Purchase #4 $88.62   10.318%   $97.7638   $97.76   $97.75   $97.80  
  Purchase #5 $41.34   10.397%   $45.6381   $45.64   $45.65   $45.60  
  Purchase #6 $213.61   6.619%   $227.7488   $227.75   $227.75   $227.70  
  Purchase #7 $110.36   10.381%   $121.8165   $121.82   $121.80   $121.80  
  7 purchase totals = $937.29       $1,033.7320   $1,033.73   $1,033.70   $1,033.70