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	$31.73	13.625%	$36.0532	$36.05	$36.05	$36.10
Purchase #2	$144.63	5.596%	$152.7235	$152.72	$152.70	$152.70
Purchase #3	$198.43	12.821%	$223.8707	$223.87	$223.85	$223.90
Purchase #4	$95.72	8.541%	$103.8954	$103.90	$103.90	$103.90
Purchase #5	$234.86	10.312%	$259.0788	$259.08	$259.10	$259.10
Purchase #6	$140.88	13.736%	$160.2313	$160.23	$160.25	$160.20
Purchase #7	$250.39	10.459%	$276.5783	$276.58	$276.60	$276.60
7 purchase totals =	$1,096.64		$1,212.4312	$1,212.43	$1,212.45	$1,212.50