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 $60.58   8.166%   $65.527   $65.53   $65.55   $65.50  
  Purchase #2 $121.96   9.243%   $133.2328   $133.23   $133.25   $133.20  
  Purchase #3 $225.28   12.689%   $253.8658   $253.87   $253.85   $253.90  
  Purchase #4 $172.37   12.368%   $193.6887   $193.69   $193.70   $193.70  
  Purchase #5 $84.32   12.649%   $94.9856   $94.99   $95.00   $95.00  
  Purchase #6 $64.28   8.104%   $69.4893   $69.49   $69.50   $69.50  
  Purchase #7 $182.63   11.166%   $203.0225   $203.02   $203.00   $203.00  
  7 purchase totals = $911.42       $1,013.8117   $1,013.82   $1,013.85   $1,013.80