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	$178.48	6.301%	$189.726	$189.73	$189.75	$189.70
Purchase #2	$173.88	4.831%	$182.2801	$182.28	$182.30	$182.30
Purchase #3	$71.81	8.397%	$77.8399	$77.84	$77.85	$77.80
Purchase #4	$238.46	9.548%	$261.2282	$261.23	$261.25	$261.20
Purchase #5	$37.62	11.256%	$41.8545	$41.85	$41.85	$41.90
Purchase #6	$114.74	4.188%	$119.5453	$119.55	$119.55	$119.50
Purchase #7	$120.49	9.425%	$131.8462	$131.85	$131.85	$131.80
7 purchase totals =	$935.48		$1,004.3202	$1,004.33	$1,004.40	$1,004.20