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	$125.73	11.594%	$140.3071	$140.31	$140.30	$140.30
Purchase #2	$159.81	4.268%	$166.6307	$166.63	$166.65	$166.60
Purchase #3	$92.54	11.732%	$103.3968	$103.40	$103.40	$103.40
Purchase #4	$185.73	4.813%	$194.6692	$194.67	$194.65	$194.70
Purchase #5	$31.38	3.740%	$32.5536	$32.55	$32.55	$32.60
Purchase #6	$10.90	8.871%	$11.8669	$11.87	$11.85	$11.90
Purchase #7	$165.59	6.654%	$176.6084	$176.61	$176.60	$176.60
7 purchase totals =	$771.68		$826.0327	$826.04	$826.00	$826.10