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	$145.31	3.317%	$150.1299	$150.13	$150.15	$150.10
Purchase #2	$82.82	8.424%	$89.7968	$89.80	$89.80	$89.80
Purchase #3	$160.91	11.279%	$179.059	$179.06	$179.05	$179.10
Purchase #4	$183.86	8.134%	$198.8152	$198.82	$198.80	$198.80
Purchase #5	$54.30	12.555%	$61.1174	$61.12	$61.10	$61.10
Purchase #6	$246.59	11.686%	$275.4065	$275.41	$275.40	$275.40
Purchase #7	$165.79	13.454%	$188.0954	$188.10	$188.10	$188.10
7 purchase totals =	$1,039.58		$1,142.4202	$1,142.44	$1,142.40	$1,142.40