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 $190.60   5.149%   $200.414   $200.41   $200.40   $200.40  
  Purchase #2 $76.63   6.513%   $81.6209   $81.62   $81.60   $81.60  
  Purchase #3 $135.77   10.701%   $150.2987   $150.30   $150.30   $150.30  
  Purchase #4 $224.92   4.774%   $235.6577   $235.66   $235.65   $235.70  
  Purchase #5 $119.54   5.367%   $125.9557   $125.96   $125.95   $126.00  
  Purchase #6 $162.53   8.576%   $176.4686   $176.47   $176.45   $176.50  
  Purchase #7 $84.38   9.364%   $92.2813   $92.28   $92.30   $92.30  
  7 purchase totals = $994.37       $1,062.6969   $1,062.70   $1,062.65   $1,062.80