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	$40.62	5.651%	$42.9154	$42.92	$42.90	$42.90
Purchase #2	$215.30	4.112%	$224.1531	$224.15	$224.15	$224.20
Purchase #3	$100.76	6.129%	$106.9356	$106.94	$106.95	$106.90
Purchase #4	$88.38	8.818%	$96.1733	$96.17	$96.15	$96.20
Purchase #5	$44.49	6.246%	$47.2688	$47.27	$47.25	$47.30
Purchase #6	$124.88	11.745%	$139.5472	$139.55	$139.55	$139.50
Purchase #7	$170.33	9.132%	$185.8845	$185.88	$185.90	$185.90
7 purchase totals =	$784.76		$842.8779	$842.88	$842.85	$842.90