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 $149.81   10.677%   $165.8052   $165.81   $165.80   $165.80  
  Purchase #2 $44.69   4.116%   $46.5294   $46.53   $46.55   $46.50  
  Purchase #3 $203.86   5.414%   $214.897   $214.90   $214.90   $214.90  
  Purchase #4 $72.56   6.290%   $77.124   $77.12   $77.10   $77.10  
  Purchase #5 $194.46   6.769%   $207.623   $207.62   $207.60   $207.60  
  Purchase #6 $138.50   9.604%   $151.8015   $151.80   $151.80   $151.80  
  Purchase #7 $195.48   3.121%   $201.5809   $201.58   $201.60   $201.60  
  7 purchase totals = $999.36       $1,065.3610   $1,065.36   $1,065.35   $1,065.30