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	$67.84	6.445%	$72.2123	$72.21	$72.20	$72.20
Purchase #2	$171.43	13.661%	$194.8491	$194.85	$194.85	$194.80
Purchase #3	$12.48	3.289%	$12.8905	$12.89	$12.90	$12.90
Purchase #4	$225.54	13.338%	$255.6225	$255.62	$255.60	$255.60
Purchase #5	$98.41	12.110%	$110.3275	$110.33	$110.35	$110.30
Purchase #6	$33.69	10.766%	$37.3171	$37.32	$37.30	$37.30
Purchase #7	$105.98	12.567%	$119.2985	$119.30	$119.30	$119.30
7 purchase totals =	$715.37		$802.5175	$802.52	$802.50	$802.40