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	$160.78	4.743%	$168.4058	$168.41	$168.40	$168.40
Purchase #2	$245.75	11.642%	$274.3602	$274.36	$274.35	$274.40
Purchase #3	$39.98	6.210%	$42.4628	$42.46	$42.45	$42.50
Purchase #4	$240.27	3.793%	$249.3834	$249.38	$249.40	$249.40
Purchase #5	$143.57	3.260%	$148.2504	$148.25	$148.25	$148.30
Purchase #6	$110.71	11.460%	$123.3974	$123.40	$123.40	$123.40
Purchase #7	$91.34	12.186%	$102.4707	$102.47	$102.45	$102.50
7 purchase totals =	$1,032.40		$1,108.7307	$1,108.73	$1,108.70	$1,108.90