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 $110.60   12.867%   $124.8309   $124.83   $124.85   $124.80  
  Purchase #2 $210.69   6.469%   $224.3195   $224.32   $224.30   $224.30  
  Purchase #3 $236.75   11.796%   $264.677   $264.68   $264.70   $264.70  
  Purchase #4 $85.85   6.671%   $91.5771   $91.58   $91.60   $91.60  
  Purchase #5 $62.94   8.381%   $68.215   $68.22   $68.20   $68.20  
  Purchase #6 $217.56   13.131%   $246.1278   $246.13   $246.15   $246.10  
  Purchase #7 $129.28   4.268%   $134.7977   $134.80   $134.80   $134.80  
  7 purchase totals = $1,053.67       $1,154.5450   $1,154.56   $1,154.60   $1,154.50