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	$82.93	7.399%	$89.066	$89.07	$89.05	$89.10
Purchase #2	$109.76	12.450%	$123.4251	$123.43	$123.45	$123.40
Purchase #3	$59.54	4.540%	$62.2431	$62.24	$62.25	$62.20
Purchase #4	$227.99	11.628%	$254.5007	$254.50	$254.50	$254.50
Purchase #5	$190.34	13.271%	$215.6	$215.60	$215.60	$215.60
Purchase #6	$76.37	4.131%	$79.5248	$79.52	$79.50	$79.50
Purchase #7	$187.93	10.148%	$207.0011	$207.00	$207.00	$207.00
7 purchase totals =	$934.86		$1,031.3608	$1,031.36	$1,031.35	$1,031.30