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	$78.32	4.795%	$82.0754	$82.08	$82.10	$82.10
Purchase #2	$69.98	9.852%	$76.8744	$76.87	$76.85	$76.90
Purchase #3	$143.47	4.455%	$149.8616	$149.86	$149.85	$149.90
Purchase #4	$195.29	4.121%	$203.3379	$203.34	$203.35	$203.30
Purchase #5	$127.38	9.170%	$139.0607	$139.06	$139.05	$139.10
Purchase #6	$171.39	12.482%	$192.7829	$192.78	$192.80	$192.80
Purchase #7	$218.63	12.439%	$245.8254	$245.83	$245.85	$245.80
7 purchase totals =	$1,004.46		$1,089.8183	$1,089.82	$1,089.85	$1,089.90