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 $86.59   13.644%   $98.4043   $98.40   $98.40   $98.40  
  Purchase #2 $195.71   7.120%   $209.6446   $209.64   $209.65   $209.60  
  Purchase #3 $69.71   8.453%   $75.6026   $75.60   $75.60   $75.60  
  Purchase #4 $237.79   5.694%   $251.3298   $251.33   $251.35   $251.30  
  Purchase #5 $237.47   12.168%   $266.3653   $266.37   $266.35   $266.40  
  Purchase #6 $109.97   11.831%   $122.9806   $122.98   $123.00   $123.00  
  Purchase #7 $98.56   3.189%   $101.7031   $101.70   $101.70   $101.70  
  7 purchase totals = $1,035.80       $1,126.0303   $1,126.02   $1,126.05   $1,126.00