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	$54.72	9.452%	$59.8921	$59.89	$59.90	$59.90
Purchase #2	$195.67	5.701%	$206.8251	$206.83	$206.85	$206.80
Purchase #3	$104.47	12.721%	$117.7596	$117.76	$117.75	$117.80
Purchase #4	$231.58	13.415%	$262.6465	$262.65	$262.65	$262.60
Purchase #5	$6.64	7.873%	$7.1628	$7.16	$7.15	$7.20
Purchase #6	$67.41	9.701%	$73.9494	$73.95	$73.95	$73.90
Purchase #7	$247.89	11.438%	$276.2437	$276.24	$276.25	$276.20
7 purchase totals =	$908.38		$1,004.4792	$1,004.48	$1,004.50	$1,004.40