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 $10.84   3.806%   $11.2526   $11.25   $11.25   $11.30  
  Purchase #2 $197.63   13.666%   $224.6381   $224.64   $224.65   $224.60  
  Purchase #3 $76.66   13.235%   $86.806   $86.81   $86.80   $86.80  
  Purchase #4 $91.92   10.687%   $101.7435   $101.74   $101.75   $101.70  
  Purchase #5 $79.46   3.279%   $82.0655   $82.07   $82.05   $82.10  
  Purchase #6 $196.84   8.232%   $213.0439   $213.04   $213.05   $213.00  
  Purchase #7 $64.50   4.589%   $67.4599   $67.46   $67.45   $67.50  
  7 purchase totals = $717.85       $787.0095   $787.01   $787.00   $787.00