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 $62.41   10.679%   $69.0748   $69.07   $69.05   $69.10  
  Purchase #2 $22.78   8.531%   $24.7234   $24.72   $24.70   $24.70  
  Purchase #3 $55.72   5.190%   $58.6119   $58.61   $58.60   $58.60  
  Purchase #4 $85.70   11.417%   $95.4844   $95.48   $95.50   $95.50  
  Purchase #5 $220.51   5.363%   $232.336   $232.34   $232.35   $232.30  
  Purchase #6 $125.83   9.600%   $137.9097   $137.91   $137.90   $137.90  
  Purchase #7 $231.77   9.359%   $253.4614   $253.46   $253.45   $253.50  
  7 purchase totals = $804.72       $871.6016   $871.59   $871.55   $871.60