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 $214.83   12.566%   $241.8255   $241.83   $241.85   $241.80  
  Purchase #2 $149.57   3.264%   $154.452   $154.45   $154.45   $154.50  
  Purchase #3 $150.98   11.545%   $168.4106   $168.41   $168.40   $168.40  
  Purchase #4 $104.86   7.517%   $112.7423   $112.74   $112.75   $112.70  
  Purchase #5 $104.91   7.558%   $112.8391   $112.84   $112.85   $112.80  
  Purchase #6 $186.32   9.864%   $204.6986   $204.70   $204.70   $204.70  
  Purchase #7 $51.72   4.818%   $54.2119   $54.21   $54.20   $54.20  
  7 purchase totals = $963.19       $1,049.1800   $1,049.18   $1,049.20   $1,049.10