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 $248.49   8.273%   $269.0476   $269.05   $269.05   $269.00  
  Purchase #2 $65.87   5.240%   $69.3216   $69.32   $69.30   $69.30  
  Purchase #3 $245.87   5.243%   $258.761   $258.76   $258.75   $258.80  
  Purchase #4 $201.88   6.668%   $215.3414   $215.34   $215.35   $215.30  
  Purchase #5 $167.57   5.544%   $176.8601   $176.86   $176.85   $176.90  
  Purchase #6 $124.49   12.576%   $140.1459   $140.15   $140.15   $140.10  
  Purchase #7 $25.75   7.182%   $27.5994   $27.60   $27.60   $27.60  
  7 purchase totals = $1,079.92       $1,157.0770   $1,157.08   $1,157.05   $1,157.00