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	$28.68	12.207%	$32.181	$32.18	$32.20	$32.20
Purchase #2	$31.31	4.828%	$32.8216	$32.82	$32.80	$32.80
Purchase #3	$134.86	4.762%	$141.282	$141.28	$141.30	$141.30
Purchase #4	$82.36	3.300%	$85.0779	$85.08	$85.10	$85.10
Purchase #5	$152.99	8.429%	$165.8855	$165.89	$165.90	$165.90
Purchase #6	$182.99	10.260%	$201.7648	$201.76	$201.75	$201.80
Purchase #7	$5.96	5.552%	$6.2909	$6.29	$6.30	$6.30
7 purchase totals =	$619.15		$665.3037	$665.30	$665.35	$665.40