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	$131.51	12.365%	$147.7712	$147.77	$147.75	$147.80
Purchase #2	$81.86	8.161%	$88.5406	$88.54	$88.55	$88.50
Purchase #3	$59.64	13.169%	$67.494	$67.49	$67.50	$67.50
Purchase #4	$74.31	5.810%	$78.6274	$78.63	$78.65	$78.60
Purchase #5	$233.36	7.641%	$251.191	$251.19	$251.20	$251.20
Purchase #6	$125.99	13.322%	$142.7744	$142.77	$142.75	$142.80
Purchase #7	$118.81	4.786%	$124.4962	$124.50	$124.50	$124.50
7 purchase totals =	$825.48		$900.8948	$900.89	$900.90	$900.90