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	$88.40	10.127%	$97.3523	$97.35	$97.35	$97.40
Purchase #2	$78.35	10.266%	$86.3934	$86.39	$86.40	$86.40
Purchase #3	$50.25	7.801%	$54.17	$54.17	$54.15	$54.20
Purchase #4	$80.91	9.804%	$88.8424	$88.84	$88.85	$88.80
Purchase #5	$127.27	12.620%	$143.3315	$143.33	$143.35	$143.30
Purchase #6	$171.40	11.261%	$190.7014	$190.70	$190.70	$190.70
Purchase #7	$86.29	4.346%	$90.0402	$90.04	$90.05	$90.00
7 purchase totals =	$682.87		$750.8312	$750.82	$750.85	$750.80