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 $223.64   13.157%   $253.0643   $253.06   $253.05   $253.10  
  Purchase #2 $34.93   6.178%   $37.088   $37.09   $37.10   $37.10  
  Purchase #3 $68.28   5.137%   $71.7875   $71.79   $71.80   $71.80  
  Purchase #4 $168.54   3.520%   $174.4726   $174.47   $174.45   $174.50  
  Purchase #5 $23.66   3.411%   $24.467   $24.47   $24.45   $24.50  
  Purchase #6 $141.57   11.159%   $157.3678   $157.37   $157.35   $157.40  
  Purchase #7 $42.86   11.230%   $47.6732   $47.67   $47.65   $47.70  
  7 purchase totals = $703.48       $765.9204   $765.92   $765.85   $766.10