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 $68.37   7.255%   $73.3302   $73.33   $73.35   $73.30  
  Purchase #2 $134.25   5.634%   $141.8136   $141.81   $141.80   $141.80  
  Purchase #3 $95.35   6.830%   $101.8624   $101.86   $101.85   $101.90  
  Purchase #4 $230.34   9.203%   $251.5382   $251.54   $251.55   $251.50  
  Purchase #5 $193.61   12.405%   $217.6273   $217.63   $217.65   $217.60  
  Purchase #6 $59.79   11.518%   $66.6766   $66.68   $66.70   $66.70  
  Purchase #7 $236.93   3.368%   $244.9098   $244.91   $244.90   $244.90  
  7 purchase totals = $1,018.64       $1,097.7581   $1,097.76   $1,097.80   $1,097.70