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 $201.69   6.116%   $214.0254   $214.03   $214.05   $214.00  
  Purchase #2 $135.83   7.587%   $146.1354   $146.14   $146.15   $146.10  
  Purchase #3 $97.36   6.836%   $104.0155   $104.02   $104.00   $104.00  
  Purchase #4 $161.30   6.590%   $171.9297   $171.93   $171.95   $171.90  
  Purchase #5 $205.80   9.746%   $225.8573   $225.86   $225.85   $225.90  
  Purchase #6 $152.86   13.525%   $173.5343   $173.53   $173.55   $173.50  
  Purchase #7 $102.81   8.158%   $111.1972   $111.20   $111.20   $111.20  
  7 purchase totals = $1,057.65       $1,146.6948   $1,146.71   $1,146.75   $1,146.60