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	$134.64	3.374%	$139.1828	$139.18	$139.20	$139.20
Purchase #2	$54.86	12.212%	$61.5595	$61.56	$61.55	$61.60
Purchase #3	$134.55	10.118%	$148.1638	$148.16	$148.15	$148.20
Purchase #4	$30.61	9.199%	$33.4258	$33.43	$33.45	$33.40
Purchase #5	$128.90	10.258%	$142.1226	$142.12	$142.10	$142.10
Purchase #6	$70.79	8.302%	$76.667	$76.67	$76.65	$76.70
Purchase #7	$50.88	12.578%	$57.2797	$57.28	$57.30	$57.30
7 purchase totals =	$605.23		$658.4012	$658.40	$658.40	$658.50