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	$74.77	4.702%	$78.2857	$78.29	$78.30	$78.30
Purchase #2	$9.86	3.820%	$10.2367	$10.24	$10.25	$10.20
Purchase #3	$142.89	3.590%	$148.0198	$148.02	$148.00	$148.00
Purchase #4	$33.57	6.760%	$35.8393	$35.84	$35.85	$35.80
Purchase #5	$37.41	9.721%	$41.0466	$41.05	$41.05	$41.00
Purchase #6	$75.26	5.111%	$79.1065	$79.11	$79.10	$79.10
Purchase #7	$68.90	13.683%	$78.3276	$78.33	$78.35	$78.30
7 purchase totals =	$442.66		$470.8622	$470.88	$470.90	$470.70