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	$68.89	4.862%	$72.2394	$72.24	$72.25	$72.20
Purchase #2	$97.50	11.115%	$108.3371	$108.34	$108.35	$108.30
Purchase #3	$190.83	9.565%	$209.0829	$209.08	$209.10	$209.10
Purchase #4	$173.39	9.516%	$189.8898	$189.89	$189.90	$189.90
Purchase #5	$110.76	8.205%	$119.8479	$119.85	$119.85	$119.80
Purchase #6	$19.91	10.508%	$22.0021	$22.00	$22.00	$22.00
Purchase #7	$46.55	9.200%	$50.8326	$50.83	$50.85	$50.80
7 purchase totals =	$707.83		$772.2318	$772.23	$772.30	$772.10