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 $152.39   5.778%   $161.1951   $161.20   $161.20   $161.20  
  Purchase #2 $59.26   13.313%   $67.1493   $67.15   $67.15   $67.10  
  Purchase #3 $184.28   10.213%   $203.1005   $203.10   $203.10   $203.10  
  Purchase #4 $46.54   3.387%   $48.1163   $48.12   $48.10   $48.10  
  Purchase #5 $224.66   8.867%   $244.5806   $244.58   $244.60   $244.60  
  Purchase #6 $170.33   12.449%   $191.5344   $191.53   $191.55   $191.50  
  Purchase #7 $127.61   9.394%   $139.5977   $139.60   $139.60   $139.60  
  7 purchase totals = $965.07       $1,055.2739   $1,055.28   $1,055.30   $1,055.20