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	$72.56	9.474%	$79.4343	$79.43	$79.45	$79.40
Purchase #2	$135.55	9.815%	$148.8542	$148.85	$148.85	$148.90
Purchase #3	$42.47	7.369%	$45.5996	$45.60	$45.60	$45.60
Purchase #4	$30.95	7.426%	$33.2483	$33.25	$33.25	$33.20
Purchase #5	$54.30	10.619%	$60.0661	$60.07	$60.05	$60.10
Purchase #6	$26.37	9.567%	$28.8928	$28.89	$28.90	$28.90
Purchase #7	$94.76	6.295%	$100.7251	$100.73	$100.75	$100.70
7 purchase totals =	$456.96		$496.8204	$496.82	$496.85	$496.80