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 $219.92   9.593%   $241.0169   $241.02   $241.00   $241.00  
  Purchase #2 $180.44   8.166%   $195.1747   $195.17   $195.15   $195.20  
  Purchase #3 $161.31   4.687%   $168.8706   $168.87   $168.85   $168.90  
  Purchase #4 $184.88   9.569%   $202.5712   $202.57   $202.55   $202.60  
  Purchase #5 $117.46   13.168%   $132.9271   $132.93   $132.95   $132.90  
  Purchase #6 $157.25   5.548%   $165.9742   $165.97   $165.95   $166.00  
  Purchase #7 $41.77   12.656%   $47.0564   $47.06   $47.05   $47.10  
  7 purchase totals = $1,063.03       $1,153.5911   $1,153.59   $1,153.50   $1,153.70