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	$45.59	8.432%	$49.4341	$49.43	$49.45	$49.40
Purchase #2	$223.45	12.113%	$250.5165	$250.52	$250.50	$250.50
Purchase #3	$232.57	3.573%	$240.8797	$240.88	$240.90	$240.90
Purchase #4	$83.63	6.849%	$89.3578	$89.36	$89.35	$89.40
Purchase #5	$79.54	7.795%	$85.7401	$85.74	$85.75	$85.70
Purchase #6	$54.79	7.451%	$58.8724	$58.87	$58.85	$58.90
Purchase #7	$223.30	7.647%	$240.3758	$240.38	$240.40	$240.40
7 purchase totals =	$942.87		$1,015.1764	$1,015.18	$1,015.20	$1,015.20