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 $237.67   10.464%   $262.5398   $262.54   $262.55   $262.50  
  Purchase #2 $26.27   5.825%   $27.8002   $27.80   $27.80   $27.80  
  Purchase #3 $150.59   7.507%   $161.8948   $161.89   $161.90   $161.90  
  Purchase #4 $246.70   8.302%   $267.181   $267.18   $267.20   $267.20  
  Purchase #5 $158.53   6.470%   $168.7869   $168.79   $168.80   $168.80  
  Purchase #6 $117.99   12.544%   $132.7907   $132.79   $132.80   $132.80  
  Purchase #7 $167.86   7.477%   $180.4109   $180.41   $180.40   $180.40  
  7 purchase totals = $1,105.61       $1,201.4043   $1,201.40   $1,201.45   $1,201.40