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	$128.27	11.727%	$143.3122	$143.31	$143.30	$143.30
Purchase #2	$141.90	5.603%	$149.8507	$149.85	$149.85	$149.90
Purchase #3	$135.30	9.510%	$148.167	$148.17	$148.15	$148.20
Purchase #4	$104.72	4.506%	$109.4387	$109.44	$109.45	$109.40
Purchase #5	$217.89	9.424%	$238.424	$238.42	$238.40	$238.40
Purchase #6	$203.63	7.387%	$218.6721	$218.67	$218.65	$218.70
Purchase #7	$168.90	6.196%	$179.365	$179.37	$179.35	$179.40
7 purchase totals =	$1,100.61		$1,187.2297	$1,187.23	$1,187.15	$1,187.30