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 $60.73   7.113%   $65.0497   $65.05   $65.05   $65.00  
  Purchase #2 $64.90   6.618%   $69.1951   $69.20   $69.20   $69.20  
  Purchase #3 $44.36   10.831%   $49.1646   $49.16   $49.15   $49.20  
  Purchase #4 $84.40   3.834%   $87.6359   $87.64   $87.65   $87.60  
  Purchase #5 $235.93   8.740%   $256.5503   $256.55   $256.55   $256.60  
  Purchase #6 $11.42   5.869%   $12.0902   $12.09   $12.10   $12.10  
  Purchase #7 $206.65   5.152%   $217.2966   $217.30   $217.30   $217.30  
  7 purchase totals = $708.39       $756.9824   $756.99   $757.00   $757.00