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 $163.25   3.357%   $168.7303   $168.73   $168.75   $168.70  
  Purchase #2 $25.57   4.220%   $26.6491   $26.65   $26.65   $26.60  
  Purchase #3 $98.55   4.835%   $103.3149   $103.31   $103.30   $103.30  
  Purchase #4 $239.96   4.132%   $249.8751   $249.88   $249.90   $249.90  
  Purchase #5 $88.84   7.813%   $95.7811   $95.78   $95.80   $95.80  
  Purchase #6 $71.46   4.296%   $74.5299   $74.53   $74.55   $74.50  
  Purchase #7 $57.39   9.240%   $62.6928   $62.69   $62.70   $62.70  
  7 purchase totals = $745.02       $781.5732   $781.57   $781.65   $781.50