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	$133.86	9.365%	$146.396	$146.40	$146.40	$146.40
Purchase #2	$56.49	5.110%	$59.3766	$59.38	$59.40	$59.40
Purchase #3	$25.96	4.787%	$27.2027	$27.20	$27.20	$27.20
Purchase #4	$145.69	11.703%	$162.7401	$162.74	$162.75	$162.70
Purchase #5	$73.76	11.625%	$82.3346	$82.33	$82.35	$82.30
Purchase #6	$92.33	12.133%	$103.5324	$103.53	$103.55	$103.50
Purchase #7	$225.69	10.117%	$248.5231	$248.52	$248.50	$248.50
7 purchase totals =	$753.78		$830.1055	$830.10	$830.15	$830.00