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 $233.96   10.306%   $258.0719   $258.07   $258.05   $258.10  
  Purchase #2 $90.98   4.784%   $95.3325   $95.33   $95.35   $95.30  
  Purchase #3 $94.79   12.353%   $106.4994   $106.50   $106.50   $106.50  
  Purchase #4 $202.70   10.501%   $223.9855   $223.99   $224.00   $224.00  
  Purchase #5 $75.79   6.533%   $80.7414   $80.74   $80.75   $80.70  
  Purchase #6 $158.70   12.116%   $177.9281   $177.93   $177.95   $177.90  
  Purchase #7 $114.61   5.708%   $121.1519   $121.15   $121.15   $121.20  
  7 purchase totals = $971.53       $1,063.7107   $1,063.71   $1,063.75   $1,063.70