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 $132.43   10.855%   $146.8053   $146.81   $146.80   $146.80  
  Purchase #2 $241.38   7.704%   $259.9759   $259.98   $260.00   $260.00  
  Purchase #3 $95.48   4.298%   $99.5837   $99.58   $99.60   $99.60  
  Purchase #4 $239.77   12.121%   $268.8325   $268.83   $268.85   $268.80  
  Purchase #5 $235.43   10.669%   $260.548   $260.55   $260.55   $260.50  
  Purchase #6 $165.41   6.506%   $176.1716   $176.17   $176.15   $176.20  
  Purchase #7 $40.56   5.285%   $42.7036   $42.70   $42.70   $42.70  
  7 purchase totals = $1,150.46       $1,254.6206   $1,254.62   $1,254.65   $1,254.60