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 $145.86   5.509%   $153.8954   $153.90   $153.90   $153.90  
  Purchase #2 $91.53   5.736%   $96.7802   $96.78   $96.80   $96.80  
  Purchase #3 $248.88   8.181%   $269.2409   $269.24   $269.25   $269.20  
  Purchase #4 $152.57   11.362%   $169.905   $169.91   $169.90   $169.90  
  Purchase #5 $34.84   12.382%   $39.1539   $39.15   $39.15   $39.20  
  Purchase #6 $219.90   6.215%   $233.5668   $233.57   $233.55   $233.60  
  Purchase #7 $73.80   10.400%   $81.4752   $81.48   $81.50   $81.50  
  7 purchase totals = $967.38       $1,044.0174   $1,044.03   $1,044.05   $1,044.10