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 $208.99   7.139%   $223.9098   $223.91   $223.90   $223.90  
  Purchase #2 $232.58   7.825%   $250.7794   $250.78   $250.80   $250.80  
  Purchase #3 $80.74   9.102%   $88.089   $88.09   $88.10   $88.10  
  Purchase #4 $83.25   5.228%   $87.6023   $87.60   $87.60   $87.60  
  Purchase #5 $227.94   9.667%   $249.975   $249.98   $250.00   $250.00  
  Purchase #6 $12.78   6.169%   $13.5684   $13.57   $13.55   $13.60  
  Purchase #7 $108.90   3.563%   $112.7801   $112.78   $112.80   $112.80  
  7 purchase totals = $955.18       $1,026.7040   $1,026.71   $1,026.75   $1,026.80