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	$101.53	8.111%	$109.7651	$109.77	$109.75	$109.80
Purchase #2	$55.75	12.830%	$62.9027	$62.90	$62.90	$62.90
Purchase #3	$221.89	7.802%	$239.2019	$239.20	$239.20	$239.20
Purchase #4	$85.94	6.688%	$91.6877	$91.69	$91.70	$91.70
Purchase #5	$78.46	13.312%	$88.9046	$88.90	$88.90	$88.90
Purchase #6	$165.65	3.488%	$171.4279	$171.43	$171.45	$171.40
Purchase #7	$232.44	9.154%	$253.7176	$253.72	$253.70	$253.70
7 purchase totals =	$941.66		$1,017.6075	$1,017.61	$1,017.60	$1,017.60