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 $232.28   5.822%   $245.8033   $245.80   $245.80   $245.80  
  Purchase #2 $181.72   11.394%   $202.4252   $202.43   $202.45   $202.40  
  Purchase #3 $69.67   5.364%   $73.4071   $73.41   $73.40   $73.40  
  Purchase #4 $152.92   4.159%   $159.2799   $159.28   $159.30   $159.30  
  Purchase #5 $101.81   10.612%   $112.6141   $112.61   $112.60   $112.60  
  Purchase #6 $119.51   7.240%   $128.1625   $128.16   $128.15   $128.20  
  Purchase #7 $149.33   8.582%   $162.1455   $162.15   $162.15   $162.10  
  7 purchase totals = $1,007.24       $1,083.8376   $1,083.84   $1,083.85   $1,083.80