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	$30.35	5.180%	$31.9221	$31.92	$31.90	$31.90
Purchase #2	$179.91	12.469%	$202.343	$202.34	$202.35	$202.30
Purchase #3	$134.59	13.359%	$152.5699	$152.57	$152.55	$152.60
Purchase #4	$183.27	9.343%	$200.3929	$200.39	$200.40	$200.40
Purchase #5	$143.40	8.111%	$155.0312	$155.03	$155.05	$155.00
Purchase #6	$93.44	13.344%	$105.9086	$105.91	$105.90	$105.90
Purchase #7	$214.94	13.203%	$243.3185	$243.32	$243.30	$243.30
7 purchase totals =	$979.90		$1,091.4862	$1,091.48	$1,091.45	$1,091.40