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	$122.27	6.206%	$129.8581	$129.86	$129.85	$129.90
Purchase #2	$21.25	11.860%	$23.7703	$23.77	$23.75	$23.80
Purchase #3	$147.48	3.166%	$152.1492	$152.15	$152.15	$152.10
Purchase #4	$149.31	12.593%	$168.1126	$168.11	$168.10	$168.10
Purchase #5	$76.39	8.589%	$82.9511	$82.95	$82.95	$83.00
Purchase #6	$67.69	6.337%	$71.9795	$71.98	$72.00	$72.00
Purchase #7	$146.27	3.688%	$151.6644	$151.66	$151.65	$151.70
7 purchase totals =	$730.66		$780.4852	$780.48	$780.45	$780.60