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	$33.56	6.550%	$35.7582	$35.76	$35.75	$35.80
Purchase #2	$27.39	12.563%	$30.831	$30.83	$30.85	$30.80
Purchase #3	$133.41	12.568%	$150.177	$150.18	$150.20	$150.20
Purchase #4	$76.91	12.488%	$86.5145	$86.51	$86.50	$86.50
Purchase #5	$117.32	13.420%	$133.0643	$133.06	$133.05	$133.10
Purchase #6	$75.29	10.240%	$82.9997	$83.00	$83.00	$83.00
Purchase #7	$61.46	10.512%	$67.9207	$67.92	$67.90	$67.90
7 purchase totals =	$525.34		$587.2654	$587.26	$587.25	$587.30