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 $164.53   13.232%   $186.3006   $186.30   $186.30   $186.30  
  Purchase #2 $74.38   6.515%   $79.2259   $79.23   $79.25   $79.20  
  Purchase #3 $234.68   9.112%   $256.064   $256.06   $256.05   $256.10  
  Purchase #4 $101.66   6.507%   $108.275   $108.28   $108.30   $108.30  
  Purchase #5 $174.86   7.534%   $188.034   $188.03   $188.05   $188.00  
  Purchase #6 $228.38   5.118%   $240.0685   $240.07   $240.05   $240.10  
  Purchase #7 $126.37   10.519%   $139.6629   $139.66   $139.65   $139.70  
  7 purchase totals = $1,104.86       $1,197.6309   $1,197.63   $1,197.65   $1,197.70