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 $229.46   11.702%   $256.3114   $256.31   $256.30   $256.30  
  Purchase #2 $69.61   8.158%   $75.2888   $75.29   $75.30   $75.30  
  Purchase #3 $223.55   11.803%   $249.9356   $249.94   $249.95   $249.90  
  Purchase #4 $58.49   5.114%   $61.4812   $61.48   $61.50   $61.50  
  Purchase #5 $176.71   12.514%   $198.8235   $198.82   $198.80   $198.80  
  Purchase #6 $163.50   6.452%   $174.049   $174.05   $174.05   $174.00  
  Purchase #7 $214.83   8.182%   $232.4074   $232.41   $232.40   $232.40  
  7 purchase totals = $1,136.15       $1,248.2969   $1,248.30   $1,248.30   $1,248.20