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 $215.35   8.572%   $233.8098   $233.81   $233.80   $233.80  
  Purchase #2 $177.39   6.292%   $188.5514   $188.55   $188.55   $188.60  
  Purchase #3 $197.35   4.811%   $206.8445   $206.84   $206.85   $206.80  
  Purchase #4 $24.44   6.678%   $26.0721   $26.07   $26.05   $26.10  
  Purchase #5 $240.48   12.662%   $270.9296   $270.93   $270.95   $270.90  
  Purchase #6 $14.92   8.113%   $16.1305   $16.13   $16.15   $16.10  
  Purchase #7 $54.93   10.384%   $60.6339   $60.63   $60.65   $60.60  
  7 purchase totals = $924.86       $1,002.9718   $1,002.96   $1,003.00   $1,002.90