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 $238.45   3.256%   $246.2139   $246.21   $246.20   $246.20  
  Purchase #2 $142.55   7.802%   $153.6718   $153.67   $153.65   $153.70  
  Purchase #3 $64.40   8.797%   $70.0653   $70.07   $70.05   $70.10  
  Purchase #4 $165.60   11.869%   $185.2551   $185.26   $185.25   $185.30  
  Purchase #5 $121.77   3.636%   $126.1976   $126.20   $126.20   $126.20  
  Purchase #6 $55.71   5.851%   $58.9696   $58.97   $58.95   $59.00  
  Purchase #7 $187.34   3.368%   $193.6496   $193.65   $193.65   $193.60  
  7 purchase totals = $975.82       $1,034.0229   $1,034.03   $1,033.95   $1,034.10