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 $206.53   12.837%   $233.0423   $233.04   $233.05   $233.00  
  Purchase #2 $238.55   8.528%   $258.8935   $258.89   $258.90   $258.90  
  Purchase #3 $171.42   9.657%   $187.974   $187.97   $187.95   $188.00  
  Purchase #4 $90.89   3.344%   $93.9294   $93.93   $93.95   $93.90  
  Purchase #5 $161.52   9.258%   $176.4735   $176.47   $176.45   $176.50  
  Purchase #6 $244.44   5.871%   $258.7911   $258.79   $258.80   $258.80  
  Purchase #7 $8.64   6.323%   $9.1863   $9.19   $9.20   $9.20  
  7 purchase totals = $1,121.99       $1,218.2901   $1,218.28   $1,218.30   $1,218.30