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	$143.81	7.325%	$154.3441	$154.34	$154.35	$154.30
Purchase #2	$238.75	12.242%	$267.9778	$267.98	$268.00	$268.00
Purchase #3	$53.83	10.647%	$59.5613	$59.56	$59.55	$59.60
Purchase #4	$209.96	11.296%	$233.6771	$233.68	$233.70	$233.70
Purchase #5	$80.77	11.242%	$89.8502	$89.85	$89.85	$89.90
Purchase #6	$55.67	7.369%	$59.7723	$59.77	$59.75	$59.80
Purchase #7	$26.31	7.828%	$28.3695	$28.37	$28.35	$28.40
7 purchase totals =	$809.10		$893.5523	$893.55	$893.55	$893.70