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 $88.46   11.831%   $98.9257   $98.93   $98.95   $98.90  
  Purchase #2 $135.92   13.467%   $154.2243   $154.22   $154.20   $154.20  
  Purchase #3 $121.51   12.646%   $136.8762   $136.88   $136.90   $136.90  
  Purchase #4 $230.42   5.130%   $242.2405   $242.24   $242.25   $242.20  
  Purchase #5 $78.46   5.201%   $82.5407   $82.54   $82.55   $82.50  
  Purchase #6 $192.94   6.518%   $205.5158   $205.52   $205.50   $205.50  
  Purchase #7 $171.77   12.571%   $193.3632   $193.36   $193.35   $193.40  
  7 purchase totals = $1,019.48       $1,113.6864   $1,113.69   $1,113.70   $1,113.60