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 $238.56   12.163%   $267.5761   $267.58   $267.60   $267.60  
  Purchase #2 $247.79   8.842%   $269.6996   $269.70   $269.70   $269.70  
  Purchase #3 $162.70   5.812%   $172.1561   $172.16   $172.15   $172.20  
  Purchase #4 $65.64   9.706%   $72.011   $72.01   $72.00   $72.00  
  Purchase #5 $14.71   5.829%   $15.5674   $15.57   $15.55   $15.60  
  Purchase #6 $214.80   13.104%   $242.9474   $242.95   $242.95   $242.90  
  Purchase #7 $166.73   3.706%   $172.909   $172.91   $172.90   $172.90  
  7 purchase totals = $1,110.93       $1,212.8666   $1,212.88   $1,212.85   $1,212.90