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	$96.61	7.528%	$103.8828	$103.88	$103.90	$103.90
Purchase #2	$5.66	11.490%	$6.3103	$6.31	$6.30	$6.30
Purchase #3	$169.74	12.266%	$190.5603	$190.56	$190.55	$190.60
Purchase #4	$64.80	10.261%	$71.4491	$71.45	$71.45	$71.40
Purchase #5	$64.29	11.390%	$71.6126	$71.61	$71.60	$71.60
Purchase #6	$9.66	7.771%	$10.4107	$10.41	$10.40	$10.40
Purchase #7	$82.96	3.367%	$85.7533	$85.75	$85.75	$85.80
7 purchase totals =	$493.72		$539.9791	$539.97	$539.95	$540.00