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	$120.87	5.470%	$127.4816	$127.48	$127.50	$127.50
Purchase #2	$129.27	12.774%	$145.7829	$145.78	$145.80	$145.80
Purchase #3	$147.51	6.351%	$156.8784	$156.88	$156.90	$156.90
Purchase #4	$99.73	3.133%	$102.8545	$102.85	$102.85	$102.90
Purchase #5	$101.32	7.744%	$109.1662	$109.17	$109.15	$109.20
Purchase #6	$161.73	11.503%	$180.3338	$180.33	$180.35	$180.30
Purchase #7	$99.71	5.119%	$104.8142	$104.81	$104.80	$104.80
7 purchase totals =	$860.14		$927.3116	$927.30	$927.35	$927.40