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 $86.85   8.141%   $93.9205   $93.92   $93.90   $93.90  
  Purchase #2 $17.82   10.494%   $19.69   $19.69   $19.70   $19.70  
  Purchase #3 $164.60   10.299%   $181.5522   $181.55   $181.55   $181.60  
  Purchase #4 $111.28   7.200%   $119.2922   $119.29   $119.30   $119.30  
  Purchase #5 $183.37   7.121%   $196.4278   $196.43   $196.45   $196.40  
  Purchase #6 $71.34   12.474%   $80.239   $80.24   $80.25   $80.20  
  Purchase #7 $163.60   5.569%   $172.7109   $172.71   $172.70   $172.70  
  7 purchase totals = $798.86       $863.8326   $863.83   $863.85   $863.80