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	$5.51	4.567%	$5.7616	$5.76	$5.75	$5.80
Purchase #2	$142.98	7.498%	$153.7006	$153.70	$153.70	$153.70
Purchase #3	$147.61	5.811%	$156.1876	$156.19	$156.20	$156.20
Purchase #4	$211.77	12.550%	$238.3471	$238.35	$238.35	$238.30
Purchase #5	$234.48	6.582%	$249.9135	$249.91	$249.90	$249.90
Purchase #6	$96.30	9.328%	$105.2829	$105.28	$105.30	$105.30
Purchase #7	$168.89	11.332%	$188.0286	$188.03	$188.05	$188.00
7 purchase totals =	$1,007.54		$1,097.2219	$1,097.22	$1,097.25	$1,097.20