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	$150.84	3.215%	$155.6895	$155.69	$155.70	$155.70
Purchase #2	$202.57	12.490%	$227.871	$227.87	$227.85	$227.90
Purchase #3	$54.85	8.115%	$59.3011	$59.30	$59.30	$59.30
Purchase #4	$239.82	10.480%	$264.9531	$264.95	$264.95	$265.00
Purchase #5	$44.59	4.234%	$46.4779	$46.48	$46.50	$46.50
Purchase #6	$234.71	5.580%	$247.8068	$247.81	$247.80	$247.80
Purchase #7	$240.72	13.741%	$273.7973	$273.80	$273.80	$273.80
7 purchase totals =	$1,168.10		$1,275.8967	$1,275.90	$1,275.90	$1,276.00