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	$244.33	12.207%	$274.1554	$274.16	$274.15	$274.20
Purchase #2	$207.46	10.490%	$229.2226	$229.22	$229.20	$229.20
Purchase #3	$59.53	12.398%	$66.9105	$66.91	$66.90	$66.90
Purchase #4	$170.70	10.156%	$188.0363	$188.04	$188.05	$188.00
Purchase #5	$70.35	11.780%	$78.6372	$78.64	$78.65	$78.60
Purchase #6	$130.34	6.666%	$139.0285	$139.03	$139.05	$139.00
Purchase #7	$77.33	13.565%	$87.8198	$87.82	$87.80	$87.80
7 purchase totals =	$960.04		$1,063.8103	$1,063.82	$1,063.80	$1,063.70