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	$123.89	11.804%	$138.514	$138.51	$138.50	$138.50
Purchase #2	$231.42	13.691%	$263.1037	$263.10	$263.10	$263.10
Purchase #3	$55.91	8.767%	$60.8116	$60.81	$60.80	$60.80
Purchase #4	$154.90	9.316%	$169.3305	$169.33	$169.35	$169.30
Purchase #5	$85.83	5.496%	$90.5472	$90.55	$90.55	$90.50
Purchase #6	$64.69	10.820%	$71.6895	$71.69	$71.70	$71.70
Purchase #7	$193.46	11.781%	$216.2515	$216.25	$216.25	$216.30
7 purchase totals =	$910.10		$1,010.2480	$1,010.24	$1,010.25	$1,010.20