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 $132.69   10.285%   $146.3372   $146.34   $146.35   $146.30  
  Purchase #2 $184.41   8.598%   $200.2656   $200.27   $200.25   $200.30  
  Purchase #3 $125.32   6.582%   $133.5686   $133.57   $133.55   $133.60  
  Purchase #4 $71.59   5.441%   $75.4852   $75.49   $75.50   $75.50  
  Purchase #5 $175.61   5.529%   $185.3195   $185.32   $185.30   $185.30  
  Purchase #6 $232.38   3.628%   $240.8107   $240.81   $240.80   $240.80  
  Purchase #7 $203.28   6.556%   $216.607   $216.61   $216.60   $216.60  
  7 purchase totals = $1,125.28       $1,198.3938   $1,198.41   $1,198.35   $1,198.40