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	$210.56	8.324%	$228.087	$228.09	$228.10	$228.10
Purchase #2	$165.38	12.234%	$185.6126	$185.61	$185.60	$185.60
Purchase #3	$222.98	7.689%	$240.1249	$240.12	$240.10	$240.10
Purchase #4	$52.59	11.835%	$58.814	$58.81	$58.80	$58.80
Purchase #5	$55.85	7.175%	$59.8572	$59.86	$59.85	$59.90
Purchase #6	$240.78	13.842%	$274.1088	$274.11	$274.10	$274.10
Purchase #7	$132.44	3.316%	$136.8317	$136.83	$136.85	$136.80
7 purchase totals =	$1,080.58		$1,183.4362	$1,183.43	$1,183.40	$1,183.40