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	$12.56	5.792%	$13.2875	$13.29	$13.30	$13.30
Purchase #2	$125.49	3.873%	$130.3502	$130.35	$130.35	$130.40
Purchase #3	$211.25	5.189%	$222.2118	$222.21	$222.20	$222.20
Purchase #4	$94.27	5.799%	$99.7367	$99.74	$99.75	$99.70
Purchase #5	$30.31	3.314%	$31.3145	$31.31	$31.30	$31.30
Purchase #6	$57.61	7.862%	$62.1393	$62.14	$62.15	$62.10
Purchase #7	$110.54	3.428%	$114.3293	$114.33	$114.35	$114.30
7 purchase totals =	$642.03		$673.3693	$673.37	$673.40	$673.30