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 $85.45   12.407%   $96.0518   $96.05   $96.05   $96.10  
  Purchase #2 $200.53   8.543%   $217.6613   $217.66   $217.65   $217.70  
  Purchase #3 $183.58   6.543%   $195.5916   $195.59   $195.60   $195.60  
  Purchase #4 $246.33   11.212%   $273.9485   $273.95   $273.95   $273.90  
  Purchase #5 $172.63   13.273%   $195.5432   $195.54   $195.55   $195.50  
  Purchase #6 $238.48   4.243%   $248.5987   $248.60   $248.60   $248.60  
  Purchase #7 $66.82   9.869%   $73.4145   $73.41   $73.40   $73.40  
  7 purchase totals = $1,193.82       $1,300.8096   $1,300.80   $1,300.80   $1,300.80