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	$237.90	13.767%	$270.6517	$270.65	$270.65	$270.70
Purchase #2	$208.25	7.255%	$223.3585	$223.36	$223.35	$223.40
Purchase #3	$200.56	7.871%	$216.3461	$216.35	$216.35	$216.30
Purchase #4	$106.35	5.132%	$111.8079	$111.81	$111.80	$111.80
Purchase #5	$150.65	13.758%	$171.3764	$171.38	$171.40	$171.40
Purchase #6	$8.81	13.137%	$9.9674	$9.97	$9.95	$10.00
Purchase #7	$128.95	10.814%	$142.8947	$142.89	$142.90	$142.90
7 purchase totals =	$1,041.47		$1,146.4027	$1,146.41	$1,146.40	$1,146.50