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 $106.39   8.615%   $115.5555   $115.56   $115.55   $115.60  
  Purchase #2 $51.92   3.126%   $53.543   $53.54   $53.55   $53.50  
  Purchase #3 $159.73   9.385%   $174.7207   $174.72   $174.70   $174.70  
  Purchase #4 $32.85   5.707%   $34.7247   $34.72   $34.70   $34.70  
  Purchase #5 $228.73   8.428%   $248.0074   $248.01   $248.00   $248.00  
  Purchase #6 $247.56   8.660%   $268.9987   $269.00   $269.00   $269.00  
  Purchase #7 $230.92   13.380%   $261.8171   $261.82   $261.80   $261.80  
  7 purchase totals = $1,058.10       $1,157.3671   $1,157.37   $1,157.30   $1,157.30