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	$30.48	8.326%	$33.0178	$33.02	$33.00	$33.00
Purchase #2	$60.70	6.533%	$64.6655	$64.67	$64.65	$64.70
Purchase #3	$242.94	5.810%	$257.0548	$257.05	$257.05	$257.10
Purchase #4	$67.54	5.630%	$71.3425	$71.34	$71.35	$71.30
Purchase #5	$215.40	3.266%	$222.435	$222.44	$222.45	$222.40
Purchase #6	$94.87	4.677%	$99.3071	$99.31	$99.30	$99.30
Purchase #7	$79.58	3.643%	$82.4791	$82.48	$82.50	$82.50
7 purchase totals =	$791.51		$830.3018	$830.31	$830.30	$830.30