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 $178.65   10.143%   $196.7705   $196.77   $196.75   $196.80  
  Purchase #2 $80.97   6.642%   $86.348   $86.35   $86.35   $86.30  
  Purchase #3 $15.46   13.531%   $17.5519   $17.55   $17.55   $17.60  
  Purchase #4 $166.25   11.494%   $185.3588   $185.36   $185.35   $185.40  
  Purchase #5 $222.73   4.503%   $232.7595   $232.76   $232.75   $232.80  
  Purchase #6 $46.31   12.815%   $52.2446   $52.24   $52.25   $52.20  
  Purchase #7 $148.55   4.391%   $155.0728   $155.07   $155.05   $155.10  
  7 purchase totals = $858.92       $926.1061   $926.10   $926.05   $926.20