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 $64.56   8.170%   $69.8346   $69.83   $69.85   $69.80  
  Purchase #2 $244.94   7.654%   $263.6877   $263.69   $263.70   $263.70  
  Purchase #3 $132.61   10.758%   $146.8762   $146.88   $146.90   $146.90  
  Purchase #4 $97.85   8.736%   $106.3982   $106.40   $106.40   $106.40  
  Purchase #5 $245.71   11.125%   $273.0452   $273.05   $273.05   $273.00  
  Purchase #6 $184.50   13.660%   $209.7027   $209.70   $209.70   $209.70  
  Purchase #7 $47.90   5.286%   $50.432   $50.43   $50.45   $50.40  
  7 purchase totals = $1,018.07       $1,119.9766   $1,119.98   $1,120.05   $1,119.90