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	$150.71	6.486%	$160.4851	$160.49	$160.50	$160.50
Purchase #2	$114.46	9.468%	$125.2971	$125.30	$125.30	$125.30
Purchase #3	$245.25	4.110%	$255.3298	$255.33	$255.35	$255.30
Purchase #4	$102.92	9.705%	$112.9084	$112.91	$112.90	$112.90
Purchase #5	$203.57	6.168%	$216.1262	$216.13	$216.15	$216.10
Purchase #6	$202.91	10.349%	$223.9092	$223.91	$223.90	$223.90
Purchase #7	$99.62	5.688%	$105.2864	$105.29	$105.30	$105.30
7 purchase totals =	$1,119.44		$1,199.3422	$1,199.36	$1,199.40	$1,199.30