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	$178.48	4.428%	$186.3831	$186.38	$186.40	$186.40
Purchase #2	$190.92	4.857%	$200.193	$200.19	$200.20	$200.20
Purchase #3	$112.25	12.830%	$126.6517	$126.65	$126.65	$126.70
Purchase #4	$180.52	4.205%	$188.1109	$188.11	$188.10	$188.10
Purchase #5	$150.96	11.658%	$168.5589	$168.56	$168.55	$168.60
Purchase #6	$110.42	12.641%	$124.3782	$124.38	$124.40	$124.40
Purchase #7	$35.73	13.327%	$40.4917	$40.49	$40.50	$40.50
7 purchase totals =	$959.28		$1,034.7675	$1,034.76	$1,034.80	$1,034.90