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	$234.96	5.361%	$247.5562	$247.56	$247.55	$247.60
Purchase #2	$159.44	7.794%	$171.8668	$171.87	$171.85	$171.90
Purchase #3	$237.57	8.842%	$258.5759	$258.58	$258.60	$258.60
Purchase #4	$245.84	3.615%	$254.7271	$254.73	$254.75	$254.70
Purchase #5	$171.47	11.455%	$191.1119	$191.11	$191.10	$191.10
Purchase #6	$59.43	9.619%	$65.1466	$65.15	$65.15	$65.10
Purchase #7	$168.50	13.271%	$190.8616	$190.86	$190.85	$190.90
7 purchase totals =	$1,277.21		$1,379.8461	$1,379.86	$1,379.85	$1,379.90