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 $184.64   11.752%   $206.3389   $206.34   $206.35   $206.30  
  Purchase #2 $161.70   5.764%   $171.0204   $171.02   $171.00   $171.00  
  Purchase #3 $145.75   5.441%   $153.6803   $153.68   $153.70   $153.70  
  Purchase #4 $44.27   4.142%   $46.1037   $46.10   $46.10   $46.10  
  Purchase #5 $71.95   9.364%   $78.6874   $78.69   $78.70   $78.70  
  Purchase #6 $17.67   6.115%   $18.7505   $18.75   $18.75   $18.80  
  Purchase #7 $82.50   3.750%   $85.5938   $85.59   $85.60   $85.60  
  7 purchase totals = $708.48       $760.1750   $760.17   $760.20   $760.20