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	$41.82	8.393%	$45.33	$45.33	$45.35	$45.30
Purchase #2	$129.97	12.597%	$146.3423	$146.34	$146.35	$146.30
Purchase #3	$128.92	10.457%	$142.4012	$142.40	$142.40	$142.40
Purchase #4	$87.71	6.320%	$93.2533	$93.25	$93.25	$93.30
Purchase #5	$30.43	3.582%	$31.52	$31.52	$31.50	$31.50
Purchase #6	$240.59	3.186%	$248.2552	$248.26	$248.25	$248.30
Purchase #7	$93.60	6.591%	$99.7692	$99.77	$99.75	$99.80
7 purchase totals =	$753.04		$806.8712	$806.87	$806.85	$806.90