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 $221.47   11.586%   $247.1295   $247.13   $247.15   $247.10  
  Purchase #2 $157.35   7.374%   $168.953   $168.95   $168.95   $169.00  
  Purchase #3 $50.68   7.413%   $54.4369   $54.44   $54.45   $54.40  
  Purchase #4 $60.49   7.438%   $64.9892   $64.99   $65.00   $65.00  
  Purchase #5 $181.63   7.538%   $195.3213   $195.32   $195.30   $195.30  
  Purchase #6 $164.74   4.713%   $172.5042   $172.50   $172.50   $172.50  
  Purchase #7 $239.31   13.488%   $271.5881   $271.59   $271.60   $271.60  
  7 purchase totals = $1,075.67       $1,174.9222   $1,174.92   $1,174.95   $1,174.90