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	$191.85	9.512%	$210.0988	$210.10	$210.10	$210.10
Purchase #2	$52.92	3.245%	$54.6373	$54.64	$54.65	$54.60
Purchase #3	$64.59	9.694%	$70.8514	$70.85	$70.85	$70.90
Purchase #4	$93.71	6.494%	$99.7955	$99.80	$99.80	$99.80
Purchase #5	$131.52	7.129%	$140.8961	$140.90	$140.90	$140.90
Purchase #6	$98.39	6.501%	$104.7863	$104.79	$104.80	$104.80
Purchase #7	$127.31	9.808%	$139.7966	$139.80	$139.80	$139.80
7 purchase totals =	$760.29		$820.8620	$820.88	$820.90	$820.90