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	$5.43	7.612%	$5.8433	$5.84	$5.85	$5.80
Purchase #2	$204.98	4.550%	$214.3066	$214.31	$214.30	$214.30
Purchase #3	$126.63	11.797%	$141.5685	$141.57	$141.55	$141.60
Purchase #4	$146.71	4.675%	$153.5687	$153.57	$153.55	$153.60
Purchase #5	$71.81	11.282%	$79.9116	$79.91	$79.90	$79.90
Purchase #6	$104.32	4.742%	$109.2669	$109.27	$109.25	$109.30
Purchase #7	$59.54	13.217%	$67.4094	$67.41	$67.40	$67.40
7 purchase totals =	$719.42		$771.8750	$771.88	$771.80	$771.90