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 $89.85   4.674%   $94.0496   $94.05   $94.05   $94.00  
  Purchase #2 $19.65   8.700%   $21.3596   $21.36   $21.35   $21.40  
  Purchase #3 $232.32   12.691%   $261.8037   $261.80   $261.80   $261.80  
  Purchase #4 $177.80   11.566%   $198.3643   $198.36   $198.35   $198.40  
  Purchase #5 $242.27   7.522%   $260.4935   $260.49   $260.50   $260.50  
  Purchase #6 $170.36   5.198%   $179.2153   $179.22   $179.20   $179.20  
  Purchase #7 $47.30   4.427%   $49.394   $49.39   $49.40   $49.40  
  7 purchase totals = $979.55       $1,064.6800   $1,064.67   $1,064.65   $1,064.70