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	$98.60	6.800%	$105.3048	$105.30	$105.30	$105.30
Purchase #2	$155.98	12.130%	$174.9004	$174.90	$174.90	$174.90
Purchase #3	$6.90	8.428%	$7.4815	$7.48	$7.50	$7.50
Purchase #4	$224.35	5.278%	$236.1912	$236.19	$236.20	$236.20
Purchase #5	$62.98	13.279%	$71.3431	$71.34	$71.35	$71.30
Purchase #6	$26.30	11.597%	$29.35	$29.35	$29.35	$29.40
Purchase #7	$39.92	12.748%	$45.009	$45.01	$45.00	$45.00
7 purchase totals =	$615.03		$669.5800	$669.57	$669.60	$669.60