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	$86.63	4.202%	$90.2702	$90.27	$90.25	$90.30
Purchase #2	$190.82	9.779%	$209.4803	$209.48	$209.50	$209.50
Purchase #3	$112.66	7.636%	$121.2627	$121.26	$121.25	$121.30
Purchase #4	$79.30	13.133%	$89.7145	$89.71	$89.70	$89.70
Purchase #5	$206.61	11.153%	$229.6532	$229.65	$229.65	$229.70
Purchase #6	$147.47	6.397%	$156.9037	$156.90	$156.90	$156.90
Purchase #7	$188.40	3.180%	$194.3911	$194.39	$194.40	$194.40
7 purchase totals =	$1,011.89		$1,091.6757	$1,091.66	$1,091.65	$1,091.80