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 $215.37   13.678%   $244.8283   $244.83   $244.85   $244.80  
  Purchase #2 $69.95   13.551%   $79.4289   $79.43   $79.45   $79.40  
  Purchase #3 $97.32   5.458%   $102.6317   $102.63   $102.65   $102.60  
  Purchase #4 $249.46   11.240%   $277.4993   $277.50   $277.50   $277.50  
  Purchase #5 $218.29   10.126%   $240.394   $240.39   $240.40   $240.40  
  Purchase #6 $49.81   11.411%   $55.4938   $55.49   $55.50   $55.50  
  Purchase #7 $96.99   11.678%   $108.3165   $108.32   $108.30   $108.30  
  7 purchase totals = $997.19       $1,108.5925   $1,108.59   $1,108.65   $1,108.50