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	$157.44	9.237%	$171.9827	$171.98	$172.00	$172.00
Purchase #2	$59.34	11.862%	$66.3789	$66.38	$66.40	$66.40
Purchase #3	$237.59	11.146%	$264.0718	$264.07	$264.05	$264.10
Purchase #4	$42.82	10.298%	$47.2296	$47.23	$47.25	$47.20
Purchase #5	$46.31	6.576%	$49.3553	$49.36	$49.35	$49.40
Purchase #6	$250.61	10.663%	$277.3325	$277.33	$277.35	$277.30
Purchase #7	$96.83	9.374%	$105.9068	$105.91	$105.90	$105.90
7 purchase totals =	$890.94		$982.2576	$982.26	$982.30	$982.30