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 $55.33   8.470%   $60.0165   $60.02   $60.00   $60.00  
  Purchase #2 $69.66   7.204%   $74.6783   $74.68   $74.70   $74.70  
  Purchase #3 $67.33   7.504%   $72.3824   $72.38   $72.40   $72.40  
  Purchase #4 $41.37   6.216%   $43.9416   $43.94   $43.95   $43.90  
  Purchase #5 $190.28   5.604%   $200.9433   $200.94   $200.95   $200.90  
  Purchase #6 $7.82   7.435%   $8.4014   $8.40   $8.40   $8.40  
  Purchase #7 $94.88   6.507%   $101.0538   $101.05   $101.05   $101.10  
  7 purchase totals = $526.67       $561.4173   $561.41   $561.45   $561.40