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	$168.46	11.593%	$187.9896	$187.99	$188.00	$188.00
Purchase #2	$245.39	11.165%	$272.7878	$272.79	$272.80	$272.80
Purchase #3	$96.61	9.602%	$105.8865	$105.89	$105.90	$105.90
Purchase #4	$82.29	9.178%	$89.8426	$89.84	$89.85	$89.80
Purchase #5	$193.82	9.544%	$212.3182	$212.32	$212.30	$212.30
Purchase #6	$37.76	6.413%	$40.1815	$40.18	$40.20	$40.20
Purchase #7	$195.32	12.719%	$220.1628	$220.16	$220.15	$220.20
7 purchase totals =	$1,019.65		$1,129.1690	$1,129.17	$1,129.20	$1,129.20