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 $194.80   9.125%   $212.5755   $212.58   $212.60   $212.60  
  Purchase #2 $246.39   3.465%   $254.9274   $254.93   $254.95   $254.90  
  Purchase #3 $202.48   5.341%   $213.2945   $213.29   $213.30   $213.30  
  Purchase #4 $184.87   12.840%   $208.6073   $208.61   $208.60   $208.60  
  Purchase #5 $183.78   11.475%   $204.8688   $204.87   $204.85   $204.90  
  Purchase #6 $36.44   13.255%   $41.2701   $41.27   $41.25   $41.30  
  Purchase #7 $201.37   12.310%   $226.1586   $226.16   $226.15   $226.20  
  7 purchase totals = $1,250.13       $1,361.7022   $1,361.71   $1,361.70   $1,361.80