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 $233.89   13.428%   $265.2967   $265.30   $265.30   $265.30  
  Purchase #2 $152.97   11.488%   $170.5432   $170.54   $170.55   $170.50  
  Purchase #3 $51.93   8.806%   $56.503   $56.50   $56.50   $56.50  
  Purchase #4 $174.28   10.490%   $192.562   $192.56   $192.55   $192.60  
  Purchase #5 $201.46   11.872%   $225.3773   $225.38   $225.40   $225.40  
  Purchase #6 $243.31   4.686%   $254.7115   $254.71   $254.70   $254.70  
  Purchase #7 $17.46   9.775%   $19.1667   $19.17   $19.15   $19.20  
  7 purchase totals = $1,075.30       $1,184.1604   $1,184.16   $1,184.15   $1,184.20