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	$224.34	3.116%	$231.3304	$231.33	$231.35	$231.30
Purchase #2	$150.26	10.512%	$166.0553	$166.06	$166.05	$166.10
Purchase #3	$166.57	7.630%	$179.2793	$179.28	$179.30	$179.30
Purchase #4	$194.53	8.111%	$210.3083	$210.31	$210.30	$210.30
Purchase #5	$37.27	5.478%	$39.3117	$39.31	$39.30	$39.30
Purchase #6	$173.37	3.727%	$179.8315	$179.83	$179.85	$179.80
Purchase #7	$103.56	5.433%	$109.1864	$109.19	$109.20	$109.20
7 purchase totals =	$1,049.90		$1,115.3029	$1,115.31	$1,115.35	$1,115.30