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	$161.69	5.809%	$171.0826	$171.08	$171.10	$171.10
Purchase #2	$238.41	7.116%	$255.3753	$255.38	$255.40	$255.40
Purchase #3	$76.29	13.729%	$86.7639	$86.76	$86.75	$86.80
Purchase #4	$13.36	5.379%	$14.0786	$14.08	$14.10	$14.10
Purchase #5	$63.52	13.253%	$71.9383	$71.94	$71.95	$71.90
Purchase #6	$28.88	11.871%	$32.3083	$32.31	$32.30	$32.30
Purchase #7	$5.39	11.318%	$6	$6.00	$6.00	$6.00
7 purchase totals =	$587.54		$637.5470	$637.55	$637.60	$637.60