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	$124.66	13.238%	$141.1625	$141.16	$141.15	$141.20
Purchase #2	$194.35	12.368%	$218.3872	$218.39	$218.40	$218.40
Purchase #3	$77.88	7.785%	$83.943	$83.94	$83.95	$83.90
Purchase #4	$231.30	8.153%	$250.1579	$250.16	$250.15	$250.20
Purchase #5	$131.85	7.629%	$141.9088	$141.91	$141.90	$141.90
Purchase #6	$6.86	5.489%	$7.2365	$7.24	$7.25	$7.20
Purchase #7	$93.96	5.237%	$98.8807	$98.88	$98.90	$98.90
7 purchase totals =	$860.86		$941.6766	$941.68	$941.70	$941.70