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	$81.46	4.481%	$85.1102	$85.11	$85.10	$85.10
Purchase #2	$196.72	4.227%	$205.0354	$205.04	$205.05	$205.00
Purchase #3	$94.63	12.562%	$106.5174	$106.52	$106.50	$106.50
Purchase #4	$46.99	10.417%	$51.8849	$51.88	$51.90	$51.90
Purchase #5	$112.27	10.498%	$124.0561	$124.06	$124.05	$124.10
Purchase #6	$49.80	10.311%	$54.9349	$54.93	$54.95	$54.90
Purchase #7	$200.78	5.309%	$211.4394	$211.44	$211.45	$211.40
7 purchase totals =	$782.65		$838.9783	$838.98	$839.00	$838.90