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 $53.71   4.230%   $55.9819   $55.98   $56.00   $56.00  
  Purchase #2 $70.43   3.469%   $72.8732   $72.87   $72.85   $72.90  
  Purchase #3 $235.26   5.431%   $248.037   $248.04   $248.05   $248.00  
  Purchase #4 $246.60   5.345%   $259.7808   $259.78   $259.80   $259.80  
  Purchase #5 $167.85   5.708%   $177.4309   $177.43   $177.45   $177.40  
  Purchase #6 $115.80   13.708%   $131.6739   $131.67   $131.65   $131.70  
  Purchase #7 $5.47   8.625%   $5.9418   $5.94   $5.95   $5.90  
  7 purchase totals = $895.12       $951.7195   $951.71   $951.75   $951.70