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	$171.30	4.127%	$178.3696	$178.37	$178.35	$178.40
Purchase #2	$90.76	13.512%	$103.0235	$103.02	$103.00	$103.00
Purchase #3	$83.26	7.605%	$89.5919	$89.59	$89.60	$89.60
Purchase #4	$121.36	4.799%	$127.1841	$127.18	$127.20	$127.20
Purchase #5	$82.81	3.327%	$85.5651	$85.57	$85.55	$85.60
Purchase #6	$145.36	11.683%	$162.3424	$162.34	$162.35	$162.30
Purchase #7	$33.88	8.360%	$36.7124	$36.71	$36.70	$36.70
7 purchase totals =	$728.73		$782.7890	$782.78	$782.75	$782.80