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	$25.63	12.713%	$28.8883	$28.89	$28.90	$28.90
Purchase #2	$244.54	5.153%	$257.1411	$257.14	$257.15	$257.10
Purchase #3	$243.73	7.112%	$261.0641	$261.06	$261.05	$261.10
Purchase #4	$221.76	5.163%	$233.2095	$233.21	$233.20	$233.20
Purchase #5	$227.30	12.454%	$255.6079	$255.61	$255.60	$255.60
Purchase #6	$41.45	5.164%	$43.5905	$43.59	$43.60	$43.60
Purchase #7	$13.46	7.550%	$14.4762	$14.48	$14.50	$14.50
7 purchase totals =	$1,017.87		$1,093.9776	$1,093.98	$1,094.00	$1,094.00