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	$142.88	11.549%	$159.3812	$159.38	$159.40	$159.40
Purchase #2	$78.64	13.853%	$89.534	$89.53	$89.55	$89.50
Purchase #3	$161.86	4.399%	$168.9802	$168.98	$169.00	$169.00
Purchase #4	$196.53	6.709%	$209.7152	$209.72	$209.70	$209.70
Purchase #5	$72.70	6.452%	$77.3906	$77.39	$77.40	$77.40
Purchase #6	$90.74	10.616%	$100.373	$100.37	$100.35	$100.40
Purchase #7	$19.81	4.334%	$20.6686	$20.67	$20.65	$20.70
7 purchase totals =	$763.16		$826.0428	$826.04	$826.05	$826.10