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	$165.88	4.221%	$172.8818	$172.88	$172.90	$172.90
Purchase #2	$182.36	4.846%	$191.1972	$191.20	$191.20	$191.20
Purchase #3	$181.94	4.475%	$190.0818	$190.08	$190.10	$190.10
Purchase #4	$246.62	3.578%	$255.4441	$255.44	$255.45	$255.40
Purchase #5	$83.48	12.432%	$93.8582	$93.86	$93.85	$93.90
Purchase #6	$54.86	12.316%	$61.6166	$61.62	$61.60	$61.60
Purchase #7	$91.41	3.730%	$94.8196	$94.82	$94.80	$94.80
7 purchase totals =	$1,006.55		$1,059.8993	$1,059.90	$1,059.90	$1,059.90