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	$238.98	13.776%	$271.9019	$271.90	$271.90	$271.90
Purchase #2	$94.50	10.541%	$104.4612	$104.46	$104.45	$104.50
Purchase #3	$228.90	4.453%	$239.0929	$239.09	$239.10	$239.10
Purchase #4	$201.99	10.401%	$222.999	$223.00	$223.00	$223.00
Purchase #5	$137.40	9.322%	$150.2084	$150.21	$150.20	$150.20
Purchase #6	$7.40	6.672%	$7.8937	$7.89	$7.90	$7.90
Purchase #7	$52.31	4.312%	$54.5656	$54.57	$54.55	$54.60
7 purchase totals =	$961.48		$1,051.1227	$1,051.12	$1,051.10	$1,051.20