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	$5.48	7.239%	$5.8767	$5.88	$5.90	$5.90
Purchase #2	$116.37	11.830%	$130.1366	$130.14	$130.15	$130.10
Purchase #3	$79.42	12.129%	$89.0529	$89.05	$89.05	$89.10
Purchase #4	$179.40	9.664%	$196.7372	$196.74	$196.75	$196.70
Purchase #5	$66.71	3.869%	$69.291	$69.29	$69.30	$69.30
Purchase #6	$153.91	11.157%	$171.0817	$171.08	$171.10	$171.10
Purchase #7	$82.44	11.333%	$91.7829	$91.78	$91.80	$91.80
7 purchase totals =	$683.73		$753.9590	$753.96	$754.05	$754.00