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	$102.53	6.696%	$109.3954	$109.40	$109.40	$109.40
Purchase #2	$178.32	10.422%	$196.9045	$196.90	$196.90	$196.90
Purchase #3	$250.36	3.415%	$258.9098	$258.91	$258.90	$258.90
Purchase #4	$38.66	4.678%	$40.4685	$40.47	$40.45	$40.50
Purchase #5	$125.88	11.770%	$140.6961	$140.70	$140.70	$140.70
Purchase #6	$49.95	5.363%	$52.6288	$52.63	$52.65	$52.60
Purchase #7	$53.58	4.410%	$55.9429	$55.94	$55.95	$55.90
7 purchase totals =	$799.28		$854.9460	$854.95	$854.95	$854.90