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	$176.30	4.335%	$183.9426	$183.94	$183.95	$183.90
Purchase #2	$250.26	8.219%	$270.8289	$270.83	$270.85	$270.80
Purchase #3	$67.54	4.551%	$70.6137	$70.61	$70.60	$70.60
Purchase #4	$227.72	5.667%	$240.6249	$240.62	$240.60	$240.60
Purchase #5	$73.25	13.220%	$82.9337	$82.93	$82.95	$82.90
Purchase #6	$161.34	6.245%	$171.4157	$171.42	$171.40	$171.40
Purchase #7	$129.90	13.700%	$147.6963	$147.70	$147.70	$147.70
7 purchase totals =	$1,086.31		$1,168.0558	$1,168.05	$1,168.05	$1,167.90