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 $112.55   10.828%   $124.7369   $124.74   $124.75   $124.70  
  Purchase #2 $182.93   4.654%   $191.4436   $191.44   $191.45   $191.40  
  Purchase #3 $148.36   3.319%   $153.2841   $153.28   $153.30   $153.30  
  Purchase #4 $199.55   11.603%   $222.7038   $222.70   $222.70   $222.70  
  Purchase #5 $108.34   4.722%   $113.4558   $113.46   $113.45   $113.50  
  Purchase #6 $122.77   12.638%   $138.2857   $138.29   $138.30   $138.30  
  Purchase #7 $206.64   5.829%   $218.685   $218.69   $218.70   $218.70  
  7 purchase totals = $1,081.14       $1,162.5949   $1,162.60   $1,162.65   $1,162.60