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	$155.94	9.591%	$170.8962	$170.90	$170.90	$170.90
Purchase #2	$16.47	12.355%	$18.5049	$18.50	$18.50	$18.50
Purchase #3	$100.53	8.839%	$109.4158	$109.42	$109.40	$109.40
Purchase #4	$85.79	5.494%	$90.5033	$90.50	$90.50	$90.50
Purchase #5	$225.40	4.331%	$235.1621	$235.16	$235.15	$235.20
Purchase #6	$27.69	9.417%	$30.2976	$30.30	$30.30	$30.30
Purchase #7	$214.90	5.684%	$227.1149	$227.11	$227.10	$227.10
7 purchase totals =	$826.72		$881.8948	$881.89	$881.85	$881.90