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	$60.51	6.502%	$64.4444	$64.44	$64.45	$64.40
Purchase #2	$81.32	12.607%	$91.572	$91.57	$91.55	$91.60
Purchase #3	$187.57	9.515%	$205.4173	$205.42	$205.40	$205.40
Purchase #4	$120.53	7.112%	$129.1021	$129.10	$129.10	$129.10
Purchase #5	$89.90	10.459%	$99.3026	$99.30	$99.30	$99.30
Purchase #6	$96.82	8.870%	$105.4079	$105.41	$105.40	$105.40
Purchase #7	$69.60	11.113%	$77.3346	$77.33	$77.35	$77.30
7 purchase totals =	$706.25		$772.5809	$772.57	$772.55	$772.50