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	$125.56	8.235%	$135.8999	$135.90	$135.90	$135.90
Purchase #2	$28.61	12.873%	$32.293	$32.29	$32.30	$32.30
Purchase #3	$75.72	5.873%	$80.167	$80.17	$80.15	$80.20
Purchase #4	$72.37	7.199%	$77.5799	$77.58	$77.60	$77.60
Purchase #5	$39.82	3.674%	$41.283	$41.28	$41.30	$41.30
Purchase #6	$96.81	6.182%	$102.7948	$102.79	$102.80	$102.80
Purchase #7	$177.31	10.821%	$196.4967	$196.50	$196.50	$196.50
7 purchase totals =	$616.20		$666.5143	$666.51	$666.55	$666.60