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	$125.69	12.665%	$141.6086	$141.61	$141.60	$141.60
Purchase #2	$110.91	12.457%	$124.7261	$124.73	$124.75	$124.70
Purchase #3	$228.96	7.220%	$245.4909	$245.49	$245.50	$245.50
Purchase #4	$226.59	13.649%	$257.5173	$257.52	$257.50	$257.50
Purchase #5	$221.61	7.811%	$238.92	$238.92	$238.90	$238.90
Purchase #6	$39.68	8.155%	$42.9159	$42.92	$42.90	$42.90
Purchase #7	$90.33	6.487%	$96.1897	$96.19	$96.20	$96.20
7 purchase totals =	$1,043.77		$1,147.3685	$1,147.38	$1,147.35	$1,147.30