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 $13.34   11.851%   $14.9209   $14.92   $14.90   $14.90  
  Purchase #2 $94.57   12.403%   $106.2995   $106.30   $106.30   $106.30  
  Purchase #3 $55.57   6.711%   $59.2993   $59.30   $59.30   $59.30  
  Purchase #4 $226.27   5.844%   $239.4932   $239.49   $239.50   $239.50  
  Purchase #5 $114.28   5.627%   $120.7105   $120.71   $120.70   $120.70  
  Purchase #6 $192.60   6.192%   $204.5258   $204.53   $204.55   $204.50  
  Purchase #7 $8.59   3.615%   $8.9005   $8.90   $8.90   $8.90  
  7 purchase totals = $705.22       $754.1497   $754.15   $754.15   $754.10