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	$162.44	7.459%	$174.5564	$174.56	$174.55	$174.60
Purchase #2	$38.86	12.813%	$43.8391	$43.84	$43.85	$43.80
Purchase #3	$220.36	13.860%	$250.9019	$250.90	$250.90	$250.90
Purchase #4	$37.42	9.534%	$40.9876	$40.99	$41.00	$41.00
Purchase #5	$90.30	4.764%	$94.6019	$94.60	$94.60	$94.60
Purchase #6	$16.42	10.680%	$18.1737	$18.17	$18.15	$18.20
Purchase #7	$18.39	11.306%	$20.4692	$20.47	$20.45	$20.50
7 purchase totals =	$584.19		$643.5298	$643.53	$643.50	$643.60