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	$74.36	5.513%	$78.4595	$78.46	$78.45	$78.50
Purchase #2	$150.54	10.173%	$165.8544	$165.85	$165.85	$165.90
Purchase #3	$26.39	11.380%	$29.3932	$29.39	$29.40	$29.40
Purchase #4	$180.74	4.360%	$188.6203	$188.62	$188.60	$188.60
Purchase #5	$40.25	5.419%	$42.4311	$42.43	$42.45	$42.40
Purchase #6	$190.91	5.628%	$201.6544	$201.65	$201.65	$201.70
Purchase #7	$120.87	12.681%	$136.1975	$136.20	$136.20	$136.20
7 purchase totals =	$784.06		$842.6104	$842.60	$842.60	$842.70