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 $113.68   10.470%   $125.5823   $125.58   $125.60   $125.60  
  Purchase #2 $229.39   9.202%   $250.4985   $250.50   $250.50   $250.50  
  Purchase #3 $148.81   8.444%   $161.3755   $161.38   $161.40   $161.40  
  Purchase #4 $62.66   11.201%   $69.6785   $69.68   $69.70   $69.70  
  Purchase #5 $38.75   5.593%   $40.9173   $40.92   $40.90   $40.90  
  Purchase #6 $163.64   5.548%   $172.7187   $172.72   $172.70   $172.70  
  Purchase #7 $216.84   8.701%   $235.7072   $235.71   $235.70   $235.70  
  7 purchase totals = $973.77       $1,056.4780   $1,056.49   $1,056.50   $1,056.50