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 $172.40   11.747%   $192.6518   $192.65   $192.65   $192.70  
  Purchase #2 $195.48   8.356%   $211.8143   $211.81   $211.80   $211.80  
  Purchase #3 $53.73   3.486%   $55.603   $55.60   $55.60   $55.60  
  Purchase #4 $67.41   9.374%   $73.729   $73.73   $73.75   $73.70  
  Purchase #5 $237.85   6.346%   $252.944   $252.94   $252.95   $252.90  
  Purchase #6 $216.72   3.823%   $225.0052   $225.01   $225.00   $225.00  
  Purchase #7 $186.40   11.612%   $208.0448   $208.04   $208.05   $208.00  
  7 purchase totals = $1,129.99       $1,219.7921   $1,219.78   $1,219.80   $1,219.70