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	$30.65	6.242%	$32.5632	$32.56	$32.55	$32.60
Purchase #2	$99.77	6.492%	$106.2471	$106.25	$106.25	$106.20
Purchase #3	$136.59	5.504%	$144.1079	$144.11	$144.10	$144.10
Purchase #4	$238.46	6.672%	$254.3701	$254.37	$254.35	$254.40
Purchase #5	$104.50	7.608%	$112.4504	$112.45	$112.45	$112.50
Purchase #6	$96.59	5.787%	$102.1797	$102.18	$102.20	$102.20
Purchase #7	$79.93	6.679%	$85.2685	$85.27	$85.25	$85.30
7 purchase totals =	$786.49		$837.1869	$837.19	$837.15	$837.30