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	$102.66	8.410%	$111.2937	$111.29	$111.30	$111.30
Purchase #2	$128.43	11.760%	$143.5334	$143.53	$143.55	$143.50
Purchase #3	$36.82	8.208%	$39.8422	$39.84	$39.85	$39.80
Purchase #4	$110.51	8.375%	$119.7652	$119.77	$119.75	$119.80
Purchase #5	$77.56	11.484%	$86.467	$86.47	$86.45	$86.50
Purchase #6	$121.50	9.758%	$133.356	$133.36	$133.35	$133.40
Purchase #7	$169.32	11.616%	$188.9882	$188.99	$189.00	$189.00
7 purchase totals =	$746.80		$823.2457	$823.25	$823.25	$823.30