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 $87.82   8.638%   $95.4059   $95.41   $95.40   $95.40  
  Purchase #2 $80.63   3.627%   $83.5545   $83.55   $83.55   $83.60  
  Purchase #3 $157.45   5.272%   $165.7508   $165.75   $165.75   $165.80  
  Purchase #4 $34.39   7.316%   $36.906   $36.91   $36.90   $36.90  
  Purchase #5 $156.64   7.245%   $167.9886   $167.99   $168.00   $168.00  
  Purchase #6 $81.47   13.387%   $92.3764   $92.38   $92.40   $92.40  
  Purchase #7 $195.79   3.416%   $202.4782   $202.48   $202.50   $202.50  
  7 purchase totals = $794.19       $844.4604   $844.47   $844.50   $844.60