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 $249.36   6.589%   $265.7903   $265.79   $265.80   $265.80  
  Purchase #2 $165.39   3.837%   $171.736   $171.74   $171.75   $171.70  
  Purchase #3 $158.51   7.490%   $170.3824   $170.38   $170.40   $170.40  
  Purchase #4 $68.46   3.530%   $70.8766   $70.88   $70.90   $70.90  
  Purchase #5 $237.29   12.309%   $266.498   $266.50   $266.50   $266.50  
  Purchase #6 $182.93   11.336%   $203.6669   $203.67   $203.65   $203.70  
  Purchase #7 $116.60   8.699%   $126.743   $126.74   $126.75   $126.70  
  7 purchase totals = $1,178.54       $1,275.6932   $1,275.70   $1,275.75   $1,275.70