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	$22.98	7.579%	$24.7217	$24.72	$24.70	$24.70
Purchase #2	$148.61	11.621%	$165.88	$165.88	$165.90	$165.90
Purchase #3	$215.73	12.113%	$241.8614	$241.86	$241.85	$241.90
Purchase #4	$148.88	5.357%	$156.8555	$156.86	$156.85	$156.90
Purchase #5	$240.88	13.250%	$272.7966	$272.80	$272.80	$272.80
Purchase #6	$213.71	3.300%	$220.7624	$220.76	$220.75	$220.80
Purchase #7	$81.78	12.427%	$91.9428	$91.94	$91.95	$91.90
7 purchase totals =	$1,072.57		$1,174.8204	$1,174.82	$1,174.80	$1,174.90