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	$249.52	10.685%	$276.1812	$276.18	$276.20	$276.20
Purchase #2	$41.56	3.252%	$42.9115	$42.91	$42.90	$42.90
Purchase #3	$70.51	11.819%	$78.8436	$78.84	$78.85	$78.80
Purchase #4	$56.82	7.580%	$61.127	$61.13	$61.15	$61.10
Purchase #5	$69.66	3.605%	$72.1712	$72.17	$72.15	$72.20
Purchase #6	$224.36	11.292%	$249.6947	$249.69	$249.70	$249.70
Purchase #7	$80.50	10.846%	$89.231	$89.23	$89.25	$89.20
7 purchase totals =	$792.93		$870.1602	$870.15	$870.20	$870.10