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 $65.55   12.527%   $73.7614   $73.76   $73.75   $73.80  
  Purchase #2 $112.90   6.569%   $120.3164   $120.32   $120.30   $120.30  
  Purchase #3 $161.56   8.138%   $174.7078   $174.71   $174.70   $174.70  
  Purchase #4 $51.97   10.447%   $57.3993   $57.40   $57.40   $57.40  
  Purchase #5 $39.76   8.152%   $43.0012   $43.00   $43.00   $43.00  
  Purchase #6 $80.87   13.567%   $91.8416   $91.84   $91.85   $91.80  
  Purchase #7 $108.67   13.186%   $122.9992   $123.00   $123.00   $123.00  
  7 purchase totals = $621.28       $684.0269   $684.03   $684.00   $684.00