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	$33.57	12.138%	$37.6447	$37.64	$37.65	$37.60
Purchase #2	$78.52	13.738%	$89.3071	$89.31	$89.30	$89.30
Purchase #3	$50.80	8.870%	$55.306	$55.31	$55.30	$55.30
Purchase #4	$57.75	3.800%	$59.9445	$59.94	$59.95	$59.90
Purchase #5	$6.97	4.425%	$7.2784	$7.28	$7.30	$7.30
Purchase #6	$58.81	9.148%	$64.1899	$64.19	$64.20	$64.20
Purchase #7	$246.32	11.206%	$273.9226	$273.92	$273.90	$273.90
7 purchase totals =	$532.74		$587.5932	$587.59	$587.60	$587.50