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 $52.49   12.627%   $59.1179   $59.12   $59.10   $59.10  
  Purchase #2 $234.69   11.460%   $261.5855   $261.59   $261.60   $261.60  
  Purchase #3 $66.25   10.735%   $73.3619   $73.36   $73.35   $73.40  
  Purchase #4 $127.51   6.643%   $135.9805   $135.98   $136.00   $136.00  
  Purchase #5 $220.40   9.329%   $240.9611   $240.96   $240.95   $241.00  
  Purchase #6 $17.96   6.186%   $19.071   $19.07   $19.05   $19.10  
  Purchase #7 $243.96   7.682%   $262.701   $262.70   $262.70   $262.70  
  7 purchase totals = $963.26       $1,052.7789   $1,052.78   $1,052.75   $1,052.90