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	$156.31	9.218%	$170.7187	$170.72	$170.70	$170.70
Purchase #2	$89.58	11.446%	$99.8333	$99.83	$99.85	$99.80
Purchase #3	$131.58	4.306%	$137.2458	$137.25	$137.25	$137.20
Purchase #4	$50.35	13.859%	$57.328	$57.33	$57.35	$57.30
Purchase #5	$238.33	3.154%	$245.8469	$245.85	$245.85	$245.80
Purchase #6	$179.34	5.329%	$188.897	$188.90	$188.90	$188.90
Purchase #7	$242.92	3.228%	$250.7615	$250.76	$250.75	$250.80
7 purchase totals =	$1,088.41		$1,150.6312	$1,150.64	$1,150.65	$1,150.50