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	$158.81	6.263%	$168.7563	$168.76	$168.75	$168.80
Purchase #2	$31.90	4.476%	$33.3278	$33.33	$33.35	$33.30
Purchase #3	$234.81	9.869%	$257.9834	$257.98	$258.00	$258.00
Purchase #4	$80.69	3.874%	$83.8159	$83.82	$83.80	$83.80
Purchase #5	$91.58	7.412%	$98.3679	$98.37	$98.35	$98.40
Purchase #6	$100.86	5.216%	$106.1209	$106.12	$106.10	$106.10
Purchase #7	$167.90	10.393%	$185.3498	$185.35	$185.35	$185.30
7 purchase totals =	$866.55		$933.7220	$933.73	$933.70	$933.70