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 $53.42   8.542%   $57.9831   $57.98   $58.00   $58.00  
  Purchase #2 $140.42   5.372%   $147.9634   $147.96   $147.95   $148.00  
  Purchase #3 $153.33   6.240%   $162.8978   $162.90   $162.90   $162.90  
  Purchase #4 $69.88   11.443%   $77.8764   $77.88   $77.90   $77.90  
  Purchase #5 $215.50   8.867%   $234.6084   $234.61   $234.60   $234.60  
  Purchase #6 $248.38   5.726%   $262.6022   $262.60   $262.60   $262.60  
  Purchase #7 $79.73   4.852%   $83.5985   $83.60   $83.60   $83.60  
  7 purchase totals = $960.66       $1,027.5298   $1,027.53   $1,027.55   $1,027.60