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	$78.31	13.850%	$89.1559	$89.16	$89.15	$89.20
Purchase #2	$125.90	8.493%	$136.5927	$136.59	$136.60	$136.60
Purchase #3	$54.97	8.133%	$59.4407	$59.44	$59.45	$59.40
Purchase #4	$149.82	3.502%	$155.0667	$155.07	$155.05	$155.10
Purchase #5	$140.79	6.534%	$149.9892	$149.99	$150.00	$150.00
Purchase #6	$125.51	5.227%	$132.0704	$132.07	$132.05	$132.10
Purchase #7	$195.98	6.846%	$209.3968	$209.40	$209.40	$209.40
7 purchase totals =	$871.28		$931.7124	$931.72	$931.70	$931.80