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	$56.71	13.148%	$64.1662	$64.17	$64.15	$64.20
Purchase #2	$148.88	11.205%	$165.562	$165.56	$165.55	$165.60
Purchase #3	$151.28	7.391%	$162.4611	$162.46	$162.45	$162.50
Purchase #4	$94.37	5.290%	$99.3622	$99.36	$99.35	$99.40
Purchase #5	$67.81	3.389%	$70.1081	$70.11	$70.10	$70.10
Purchase #6	$201.64	5.771%	$213.2766	$213.28	$213.30	$213.30
Purchase #7	$43.80	5.690%	$46.2922	$46.29	$46.30	$46.30
7 purchase totals =	$764.49		$821.2284	$821.23	$821.20	$821.40