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	$113.29	6.414%	$120.5564	$120.56	$120.55	$120.60
Purchase #2	$156.76	7.771%	$168.9418	$168.94	$168.95	$168.90
Purchase #3	$75.35	10.403%	$83.1887	$83.19	$83.20	$83.20
Purchase #4	$210.46	11.817%	$235.3301	$235.33	$235.35	$235.30
Purchase #5	$210.40	6.111%	$223.2575	$223.26	$223.25	$223.30
Purchase #6	$91.81	11.260%	$102.1478	$102.15	$102.15	$102.10
Purchase #7	$59.68	12.550%	$67.1698	$67.17	$67.15	$67.20
7 purchase totals =	$917.75		$1,000.5921	$1,000.60	$1,000.60	$1,000.60