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	$76.51	7.274%	$82.0753	$82.08	$82.10	$82.10
Purchase #2	$81.47	9.494%	$89.2048	$89.20	$89.20	$89.20
Purchase #3	$146.99	8.204%	$159.0491	$159.05	$159.05	$159.00
Purchase #4	$123.72	3.103%	$127.559	$127.56	$127.55	$127.60
Purchase #5	$213.47	4.187%	$222.408	$222.41	$222.40	$222.40
Purchase #6	$232.63	5.643%	$245.7573	$245.76	$245.75	$245.80
Purchase #7	$172.55	11.165%	$191.8152	$191.82	$191.80	$191.80
7 purchase totals =	$1,047.34		$1,117.8687	$1,117.88	$1,117.85	$1,117.90