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	$87.89	13.618%	$99.8589	$99.86	$99.85	$99.90
Purchase #2	$249.48	13.413%	$282.9428	$282.94	$282.95	$282.90
Purchase #3	$196.88	10.145%	$216.8535	$216.85	$216.85	$216.90
Purchase #4	$118.32	7.282%	$126.9361	$126.94	$126.95	$126.90
Purchase #5	$68.46	12.777%	$77.2071	$77.21	$77.20	$77.20
Purchase #6	$150.27	3.730%	$155.8751	$155.88	$155.90	$155.90
Purchase #7	$130.33	5.539%	$137.549	$137.55	$137.55	$137.50
7 purchase totals =	$1,001.63		$1,097.2225	$1,097.23	$1,097.25	$1,097.20