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	$88.29	3.386%	$91.2795	$91.28	$91.30	$91.30
Purchase #2	$92.31	3.369%	$95.4199	$95.42	$95.40	$95.40
Purchase #3	$229.65	8.778%	$249.8087	$249.81	$249.80	$249.80
Purchase #4	$164.51	12.306%	$184.7546	$184.75	$184.75	$184.80
Purchase #5	$72.92	12.785%	$82.2428	$82.24	$82.25	$82.20
Purchase #6	$19.25	10.654%	$21.3009	$21.30	$21.30	$21.30
Purchase #7	$148.80	10.632%	$164.6204	$164.62	$164.60	$164.60
7 purchase totals =	$815.73		$889.4268	$889.42	$889.40	$889.40