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 $211.61   12.271%   $237.5767   $237.58   $237.60   $237.60  
  Purchase #2 $93.45   10.196%   $102.9782   $102.98   $103.00   $103.00  
  Purchase #3 $175.80   8.277%   $190.351   $190.35   $190.35   $190.40  
  Purchase #4 $164.30   4.742%   $172.0911   $172.09   $172.10   $172.10  
  Purchase #5 $24.80   10.289%   $27.3517   $27.35   $27.35   $27.40  
  Purchase #6 $19.90   11.775%   $22.2432   $22.24   $22.25   $22.20  
  Purchase #7 $246.89   10.408%   $272.5863   $272.59   $272.60   $272.60  
  7 purchase totals = $936.75       $1,025.1782   $1,025.18   $1,025.25   $1,025.30