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 $141.32   6.188%   $150.0649   $150.06   $150.05   $150.10  
  Purchase #2 $246.84   4.651%   $258.3205   $258.32   $258.30   $258.30  
  Purchase #3 $178.31   5.800%   $188.652   $188.65   $188.65   $188.70  
  Purchase #4 $82.70   12.455%   $93.0003   $93.00   $93.00   $93.00  
  Purchase #5 $196.74   12.291%   $220.9213   $220.92   $220.90   $220.90  
  Purchase #6 $44.94   6.164%   $47.7101   $47.71   $47.70   $47.70  
  Purchase #7 $228.37   8.177%   $247.0438   $247.04   $247.05   $247.00  
  7 purchase totals = $1,119.22       $1,205.7129   $1,205.70   $1,205.65   $1,205.70