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 $108.47   5.686%   $114.6376   $114.64   $114.65   $114.60  
  Purchase #2 $124.50   8.352%   $134.8982   $134.90   $134.90   $134.90  
  Purchase #3 $107.85   12.633%   $121.4747   $121.47   $121.45   $121.50  
  Purchase #4 $128.95   3.561%   $133.5419   $133.54   $133.55   $133.50  
  Purchase #5 $31.62   6.781%   $33.7642   $33.76   $33.75   $33.80  
  Purchase #6 $132.47   5.872%   $140.2486   $140.25   $140.25   $140.20  
  Purchase #7 $225.52   6.251%   $239.6173   $239.62   $239.60   $239.60  
  7 purchase totals = $859.38       $918.1825   $918.18   $918.15   $918.10