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 $93.62   5.241%   $98.5266   $98.53   $98.55   $98.50  
  Purchase #2 $26.57   4.267%   $27.7037   $27.70   $27.70   $27.70  
  Purchase #3 $165.45   4.260%   $172.4982   $172.50   $172.50   $172.50  
  Purchase #4 $179.48   3.755%   $186.2195   $186.22   $186.20   $186.20  
  Purchase #5 $214.47   10.564%   $237.1266   $237.13   $237.15   $237.10  
  Purchase #6 $154.79   4.339%   $161.5063   $161.51   $161.50   $161.50  
  Purchase #7 $142.87   11.177%   $158.8386   $158.84   $158.85   $158.80  
  7 purchase totals = $977.25       $1,042.4195   $1,042.43   $1,042.45   $1,042.30