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	$76.27	5.261%	$80.2826	$80.28	$80.30	$80.30
Purchase #2	$72.54	12.192%	$81.3841	$81.38	$81.40	$81.40
Purchase #3	$101.84	8.316%	$110.309	$110.31	$110.30	$110.30
Purchase #4	$85.72	5.259%	$90.228	$90.23	$90.25	$90.20
Purchase #5	$221.99	12.457%	$249.6433	$249.64	$249.65	$249.60
Purchase #6	$87.29	13.636%	$99.1929	$99.19	$99.20	$99.20
Purchase #7	$157.55	3.182%	$162.5632	$162.56	$162.55	$162.60
7 purchase totals =	$803.20		$873.6031	$873.59	$873.65	$873.60