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 $61.67   6.866%   $65.9043   $65.90   $65.90   $65.90  
  Purchase #2 $97.34   6.857%   $104.0146   $104.01   $104.00   $104.00  
  Purchase #3 $125.40   13.848%   $142.7654   $142.77   $142.75   $142.80  
  Purchase #4 $151.31   8.257%   $163.8037   $163.80   $163.80   $163.80  
  Purchase #5 $22.70   10.158%   $25.0059   $25.01   $25.00   $25.00  
  Purchase #6 $245.28   5.552%   $258.8979   $258.90   $258.90   $258.90  
  Purchase #7 $222.60   12.699%   $250.868   $250.87   $250.85   $250.90  
  7 purchase totals = $926.30       $1,011.2598   $1,011.26   $1,011.20   $1,011.30