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	$137.89	13.299%	$156.228	$156.23	$156.25	$156.20
Purchase #2	$127.41	10.523%	$140.8174	$140.82	$140.80	$140.80
Purchase #3	$208.34	5.649%	$220.1091	$220.11	$220.10	$220.10
Purchase #4	$41.63	9.278%	$45.4924	$45.49	$45.50	$45.50
Purchase #5	$245.34	9.140%	$267.7641	$267.76	$267.75	$267.80
Purchase #6	$203.36	12.132%	$228.0316	$228.03	$228.05	$228.00
Purchase #7	$73.60	11.508%	$82.0699	$82.07	$82.05	$82.10
7 purchase totals =	$1,037.57		$1,140.5125	$1,140.51	$1,140.50	$1,140.50