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	$139.80	11.268%	$155.5527	$155.55	$155.55	$155.60
Purchase #2	$228.46	7.287%	$245.1079	$245.11	$245.10	$245.10
Purchase #3	$27.61	13.545%	$31.3498	$31.35	$31.35	$31.30
Purchase #4	$171.56	4.201%	$178.7672	$178.77	$178.75	$178.80
Purchase #5	$169.67	13.123%	$191.9358	$191.94	$191.95	$191.90
Purchase #6	$170.52	5.464%	$179.8372	$179.84	$179.85	$179.80
Purchase #7	$41.90	9.280%	$45.7883	$45.79	$45.80	$45.80
7 purchase totals =	$949.52		$1,028.3389	$1,028.35	$1,028.35	$1,028.30