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	$54.41	8.148%	$58.8433	$58.84	$58.85	$58.80
Purchase #2	$213.64	3.594%	$221.3182	$221.32	$221.30	$221.30
Purchase #3	$104.34	6.834%	$111.4706	$111.47	$111.45	$111.50
Purchase #4	$20.77	3.235%	$21.4419	$21.44	$21.45	$21.40
Purchase #5	$125.47	7.484%	$134.8602	$134.86	$134.85	$134.90
Purchase #6	$168.63	10.119%	$185.6937	$185.69	$185.70	$185.70
Purchase #7	$52.88	8.299%	$57.2685	$57.27	$57.25	$57.30
7 purchase totals =	$740.14		$790.8964	$790.89	$790.85	$790.90