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	$53.71	8.687%	$58.3758	$58.38	$58.40	$58.40
Purchase #2	$165.95	13.796%	$188.8445	$188.84	$188.85	$188.80
Purchase #3	$56.41	6.199%	$59.9069	$59.91	$59.90	$59.90
Purchase #4	$166.54	9.687%	$182.6727	$182.67	$182.65	$182.70
Purchase #5	$81.61	8.439%	$88.4971	$88.50	$88.50	$88.50
Purchase #6	$150.53	6.462%	$160.2572	$160.26	$160.25	$160.30
Purchase #7	$174.28	3.233%	$179.9145	$179.91	$179.90	$179.90
7 purchase totals =	$849.03		$918.4687	$918.47	$918.45	$918.50