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	$133.80	8.368%	$144.9964	$145.00	$145.00	$145.00
Purchase #2	$36.40	8.524%	$39.5027	$39.50	$39.50	$39.50
Purchase #3	$92.76	5.171%	$97.5566	$97.56	$97.55	$97.60
Purchase #4	$78.48	13.565%	$89.1258	$89.13	$89.15	$89.10
Purchase #5	$85.40	4.256%	$89.0346	$89.03	$89.05	$89.00
Purchase #6	$171.61	7.515%	$184.5065	$184.51	$184.50	$184.50
Purchase #7	$240.39	6.206%	$255.3086	$255.31	$255.30	$255.30
7 purchase totals =	$838.84		$900.0312	$900.04	$900.05	$900.00