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	$78.64	5.675%	$83.1028	$83.10	$83.10	$83.10
Purchase #2	$141.28	7.535%	$151.9254	$151.93	$151.95	$151.90
Purchase #3	$5.48	9.790%	$6.0165	$6.02	$6.00	$6.00
Purchase #4	$249.90	11.793%	$279.3707	$279.37	$279.35	$279.40
Purchase #5	$215.25	3.397%	$222.562	$222.56	$222.55	$222.60
Purchase #6	$63.95	11.402%	$71.2416	$71.24	$71.25	$71.20
Purchase #7	$71.44	8.223%	$77.3145	$77.31	$77.30	$77.30
7 purchase totals =	$825.94		$891.5335	$891.53	$891.50	$891.50