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 $196.62   5.407%   $207.2512   $207.25   $207.25   $207.30  
  Purchase #2 $45.81   12.671%   $51.6146   $51.61   $51.60   $51.60  
  Purchase #3 $59.83   5.235%   $62.9621   $62.96   $62.95   $63.00  
  Purchase #4 $199.63   9.224%   $218.0439   $218.04   $218.05   $218.00  
  Purchase #5 $152.42   8.447%   $165.2949   $165.29   $165.30   $165.30  
  Purchase #6 $194.87   6.332%   $207.2092   $207.21   $207.20   $207.20  
  Purchase #7 $16.33   12.326%   $18.3428   $18.34   $18.35   $18.30  
  7 purchase totals = $865.51       $930.7187   $930.70   $930.70   $930.70