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	$174.75	6.425%	$185.9777	$185.98	$186.00	$186.00
Purchase #2	$250.63	12.165%	$281.1191	$281.12	$281.10	$281.10
Purchase #3	$183.61	6.320%	$195.2142	$195.21	$195.20	$195.20
Purchase #4	$143.40	10.793%	$158.8772	$158.88	$158.90	$158.90
Purchase #5	$102.25	10.748%	$113.2398	$113.24	$113.25	$113.20
Purchase #6	$53.41	12.214%	$59.9335	$59.93	$59.95	$59.90
Purchase #7	$70.60	11.514%	$78.7289	$78.73	$78.75	$78.70
7 purchase totals =	$978.65		$1,073.0904	$1,073.09	$1,073.15	$1,073.00