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	$128.53	13.847%	$146.3275	$146.33	$146.35	$146.30
Purchase #2	$245.86	10.346%	$271.2967	$271.30	$271.30	$271.30
Purchase #3	$195.59	13.219%	$221.445	$221.45	$221.45	$221.40
Purchase #4	$129.54	3.804%	$134.4677	$134.47	$134.45	$134.50
Purchase #5	$73.44	9.680%	$80.549	$80.55	$80.55	$80.50
Purchase #6	$93.29	11.831%	$104.3271	$104.33	$104.35	$104.30
Purchase #7	$87.51	5.136%	$92.0045	$92.00	$92.00	$92.00
7 purchase totals =	$953.76		$1,050.4175	$1,050.43	$1,050.45	$1,050.30