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	$131.91	3.237%	$136.1799	$136.18	$136.20	$136.20
Purchase #2	$146.31	3.713%	$151.7425	$151.74	$151.75	$151.70
Purchase #3	$79.92	11.339%	$88.9821	$88.98	$89.00	$89.00
Purchase #4	$144.28	4.327%	$150.523	$150.52	$150.50	$150.50
Purchase #5	$218.76	11.339%	$243.5652	$243.57	$243.55	$243.60
Purchase #6	$25.45	7.168%	$27.2743	$27.27	$27.25	$27.30
Purchase #7	$76.53	3.824%	$79.4565	$79.46	$79.45	$79.50
7 purchase totals =	$823.16		$877.7235	$877.72	$877.70	$877.80