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	$239.79	9.351%	$262.2128	$262.21	$262.20	$262.20
Purchase #2	$156.76	5.634%	$165.5919	$165.59	$165.60	$165.60
Purchase #3	$225.71	6.713%	$240.8619	$240.86	$240.85	$240.90
Purchase #4	$45.81	5.459%	$48.3108	$48.31	$48.30	$48.30
Purchase #5	$31.31	13.200%	$35.4429	$35.44	$35.45	$35.40
Purchase #6	$73.31	9.819%	$80.5083	$80.51	$80.50	$80.50
Purchase #7	$6.72	9.822%	$7.38	$7.38	$7.40	$7.40
7 purchase totals =	$779.41		$840.3086	$840.30	$840.30	$840.30