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 $208.29   6.641%   $222.1225   $222.12   $222.10   $222.10  
  Purchase #2 $174.83   4.423%   $182.5627   $182.56   $182.55   $182.60  
  Purchase #3 $150.99   5.612%   $159.4636   $159.46   $159.45   $159.50  
  Purchase #4 $186.29   12.164%   $208.9503   $208.95   $208.95   $209.00  
  Purchase #5 $178.87   9.388%   $195.6623   $195.66   $195.65   $195.70  
  Purchase #6 $244.68   5.164%   $257.3153   $257.32   $257.30   $257.30  
  Purchase #7 $141.80   4.256%   $147.835   $147.84   $147.85   $147.80  
  7 purchase totals = $1,285.75       $1,373.9117   $1,373.91   $1,373.85   $1,374.00