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 $216.47   10.531%   $239.2665   $239.27   $239.25   $239.30  
  Purchase #2 $208.49   7.750%   $224.648   $224.65   $224.65   $224.60  
  Purchase #3 $13.40   8.560%   $14.547   $14.55   $14.55   $14.50  
  Purchase #4 $186.28   11.507%   $207.7152   $207.72   $207.70   $207.70  
  Purchase #5 $212.71   10.199%   $234.4043   $234.40   $234.40   $234.40  
  Purchase #6 $212.97   11.774%   $238.0451   $238.05   $238.05   $238.00  
  Purchase #7 $102.50   11.584%   $114.3736   $114.37   $114.35   $114.40  
  7 purchase totals = $1,152.82       $1,272.9997   $1,273.01   $1,272.95   $1,272.90