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 $91.73   7.458%   $98.5712   $98.57   $98.55   $98.60  
  Purchase #2 $182.72   11.479%   $203.6944   $203.69   $203.70   $203.70  
  Purchase #3 $80.65   10.220%   $88.8924   $88.89   $88.90   $88.90  
  Purchase #4 $125.63   6.284%   $133.5246   $133.52   $133.50   $133.50  
  Purchase #5 $217.36   11.574%   $242.5172   $242.52   $242.50   $242.50  
  Purchase #6 $72.34   12.355%   $81.2776   $81.28   $81.30   $81.30  
  Purchase #7 $184.58   10.425%   $203.8225   $203.82   $203.80   $203.80  
  7 purchase totals = $955.01       $1,052.2999   $1,052.29   $1,052.25   $1,052.30