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	$10.56	3.138%	$10.8914	$10.89	$10.90	$10.90
Purchase #2	$181.30	4.455%	$189.3769	$189.38	$189.40	$189.40
Purchase #3	$179.91	5.564%	$189.9202	$189.92	$189.90	$189.90
Purchase #4	$57.59	7.433%	$61.8707	$61.87	$61.85	$61.90
Purchase #5	$232.79	5.580%	$245.7797	$245.78	$245.80	$245.80
Purchase #6	$196.40	13.192%	$222.3091	$222.31	$222.30	$222.30
Purchase #7	$83.62	3.489%	$86.5375	$86.54	$86.55	$86.50
7 purchase totals =	$942.17		$1,006.6855	$1,006.69	$1,006.70	$1,006.70