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	$130.34	7.553%	$140.1846	$140.18	$140.20	$140.20
Purchase #2	$104.78	6.624%	$111.7206	$111.72	$111.70	$111.70
Purchase #3	$110.35	8.113%	$119.3027	$119.30	$119.30	$119.30
Purchase #4	$7.61	6.698%	$8.1197	$8.12	$8.10	$8.10
Purchase #5	$75.96	12.549%	$85.4922	$85.49	$85.50	$85.50
Purchase #6	$41.95	3.448%	$43.3964	$43.40	$43.40	$43.40
Purchase #7	$58.29	12.121%	$65.3553	$65.36	$65.35	$65.40
7 purchase totals =	$529.28		$573.5715	$573.57	$573.55	$573.60