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 $111.43   12.615%   $125.4869   $125.49   $125.50   $125.50  
  Purchase #2 $55.95   4.762%   $58.6143   $58.61   $58.60   $58.60  
  Purchase #3 $40.45   8.732%   $43.9821   $43.98   $44.00   $44.00  
  Purchase #4 $218.50   12.801%   $246.4702   $246.47   $246.45   $246.50  
  Purchase #5 $194.72   4.396%   $203.2799   $203.28   $203.30   $203.30  
  Purchase #6 $119.79   6.794%   $127.9285   $127.93   $127.95   $127.90  
  Purchase #7 $248.88   8.769%   $270.7043   $270.70   $270.70   $270.70  
  7 purchase totals = $989.72       $1,076.4662   $1,076.46   $1,076.50   $1,076.50