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 $51.52   7.609%   $55.4402   $55.44   $55.45   $55.40  
  Purchase #2 $128.86   9.137%   $140.6339   $140.63   $140.65   $140.60  
  Purchase #3 $47.60   8.619%   $51.7026   $51.70   $51.70   $51.70  
  Purchase #4 $216.48   5.445%   $228.2673   $228.27   $228.25   $228.30  
  Purchase #5 $139.95   9.236%   $152.8758   $152.88   $152.90   $152.90  
  Purchase #6 $166.30   3.238%   $171.6848   $171.68   $171.70   $171.70  
  Purchase #7 $215.61   4.588%   $225.5022   $225.50   $225.50   $225.50  
  7 purchase totals = $966.32       $1,026.1068   $1,026.10   $1,026.15   $1,026.10