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	$70.70	10.300%	$77.9821	$77.98	$78.00	$78.00
Purchase #2	$111.68	11.301%	$124.301	$124.30	$124.30	$124.30
Purchase #3	$150.85	7.815%	$162.6389	$162.64	$162.65	$162.60
Purchase #4	$28.63	13.693%	$32.5503	$32.55	$32.55	$32.60
Purchase #5	$104.43	6.764%	$111.4936	$111.49	$111.50	$111.50
Purchase #6	$154.41	8.482%	$167.5071	$167.51	$167.50	$167.50
Purchase #7	$150.65	6.433%	$160.3413	$160.34	$160.35	$160.30
7 purchase totals =	$771.35		$836.8143	$836.81	$836.85	$836.80