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 $87.38   8.706%   $94.9873   $94.99   $95.00   $95.00  
  Purchase #2 $97.28   8.822%   $105.862   $105.86   $105.85   $105.90  
  Purchase #3 $161.91   11.110%   $179.8982   $179.90   $179.90   $179.90  
  Purchase #4 $57.37   10.370%   $63.3193   $63.32   $63.30   $63.30  
  Purchase #5 $100.43   4.476%   $104.9252   $104.93   $104.95   $104.90  
  Purchase #6 $132.57   5.739%   $140.1782   $140.18   $140.20   $140.20  
  Purchase #7 $248.70   13.315%   $281.8144   $281.81   $281.80   $281.80  
  7 purchase totals = $885.64       $970.9846   $970.99   $971.00   $971.00