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 $239.41   10.160%   $263.7341   $263.73   $263.75   $263.70  
  Purchase #2 $60.26   6.140%   $63.96   $63.96   $63.95   $64.00  
  Purchase #3 $200.68   4.851%   $210.415   $210.42   $210.40   $210.40  
  Purchase #4 $76.38   5.154%   $80.3166   $80.32   $80.30   $80.30  
  Purchase #5 $212.46   11.502%   $236.8971   $236.90   $236.90   $236.90  
  Purchase #6 $214.36   12.116%   $240.3319   $240.33   $240.35   $240.30  
  Purchase #7 $45.28   9.492%   $49.578   $49.58   $49.60   $49.60  
  7 purchase totals = $1,048.83       $1,145.2327   $1,145.24   $1,145.25   $1,145.20