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 $61.44   7.272%   $65.9079   $65.91   $65.90   $65.90  
  Purchase #2 $98.92   4.702%   $103.5712   $103.57   $103.55   $103.60  
  Purchase #3 $212.45   5.242%   $223.5866   $223.59   $223.60   $223.60  
  Purchase #4 $150.59   6.773%   $160.7895   $160.79   $160.80   $160.80  
  Purchase #5 $84.89   11.408%   $94.5743   $94.57   $94.55   $94.60  
  Purchase #6 $55.36   8.611%   $60.127   $60.13   $60.15   $60.10  
  Purchase #7 $115.87   3.264%   $119.652   $119.65   $119.65   $119.70  
  7 purchase totals = $779.52       $828.2085   $828.21   $828.20   $828.30