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	$100.31	9.566%	$109.9057	$109.91	$109.90	$109.90
Purchase #2	$201.46	5.316%	$212.1696	$212.17	$212.15	$212.20
Purchase #3	$156.57	7.242%	$167.9088	$167.91	$167.90	$167.90
Purchase #4	$39.62	6.856%	$42.3363	$42.34	$42.35	$42.30
Purchase #5	$165.49	9.151%	$180.634	$180.63	$180.65	$180.60
Purchase #6	$102.32	4.729%	$107.1587	$107.16	$107.15	$107.20
Purchase #7	$150.53	6.231%	$159.9095	$159.91	$159.90	$159.90
7 purchase totals =	$916.30		$980.0226	$980.03	$980.00	$980.00