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	$74.43	5.869%	$78.7983	$78.80	$78.80	$78.80
Purchase #2	$39.69	4.366%	$41.4229	$41.42	$41.40	$41.40
Purchase #3	$49.46	7.520%	$53.1794	$53.18	$53.20	$53.20
Purchase #4	$219.27	13.146%	$248.0952	$248.10	$248.10	$248.10
Purchase #5	$59.34	4.289%	$61.8851	$61.89	$61.90	$61.90
Purchase #6	$27.31	3.704%	$28.3216	$28.32	$28.30	$28.30
Purchase #7	$147.66	8.572%	$160.3174	$160.32	$160.30	$160.30
7 purchase totals =	$617.16		$672.0199	$672.03	$672.00	$672.00