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	$141.59	4.309%	$147.6911	$147.69	$147.70	$147.70
Purchase #2	$250.71	6.819%	$267.8059	$267.81	$267.80	$267.80
Purchase #3	$189.83	5.409%	$200.0979	$200.10	$200.10	$200.10
Purchase #4	$187.46	3.816%	$194.6135	$194.61	$194.60	$194.60
Purchase #5	$70.85	11.296%	$78.8532	$78.85	$78.85	$78.90
Purchase #6	$162.58	11.183%	$180.7613	$180.76	$180.75	$180.80
Purchase #7	$18.67	13.656%	$21.2196	$21.22	$21.20	$21.20
7 purchase totals =	$1,021.69		$1,091.0425	$1,091.04	$1,091.00	$1,091.10