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	$72.71	13.449%	$82.4888	$82.49	$82.50	$82.50
Purchase #2	$115.47	12.538%	$129.9476	$129.95	$129.95	$129.90
Purchase #3	$64.48	11.508%	$71.9004	$71.90	$71.90	$71.90
Purchase #4	$22.42	7.872%	$24.1849	$24.18	$24.20	$24.20
Purchase #5	$85.82	4.156%	$89.3867	$89.39	$89.40	$89.40
Purchase #6	$172.37	6.736%	$183.9808	$183.98	$184.00	$184.00
Purchase #7	$71.46	5.157%	$75.1452	$75.15	$75.15	$75.10
7 purchase totals =	$604.73		$657.0344	$657.04	$657.10	$657.00