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 $107.39   6.258%   $114.1105   $114.11   $114.10   $114.10  
  Purchase #2 $207.47   12.767%   $233.9577   $233.96   $233.95   $234.00  
  Purchase #3 $157.47   11.769%   $176.0026   $176.00   $176.00   $176.00  
  Purchase #4 $134.83   12.196%   $151.2739   $151.27   $151.25   $151.30  
  Purchase #5 $87.96   8.327%   $95.2844   $95.28   $95.30   $95.30  
  Purchase #6 $154.79   3.691%   $160.5033   $160.50   $160.50   $160.50  
  Purchase #7 $130.25   12.679%   $146.7644   $146.76   $146.75   $146.80  
  7 purchase totals = $980.16       $1,077.8968   $1,077.88   $1,077.85   $1,078.00