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	$56.35	5.442%	$59.4166	$59.42	$59.40	$59.40
Purchase #2	$84.90	4.299%	$88.5499	$88.55	$88.55	$88.50
Purchase #3	$226.46	7.525%	$243.5011	$243.50	$243.50	$243.50
Purchase #4	$19.42	4.113%	$20.2187	$20.22	$20.20	$20.20
Purchase #5	$69.63	8.353%	$75.4462	$75.45	$75.45	$75.40
Purchase #6	$90.91	9.506%	$99.5519	$99.55	$99.55	$99.60
Purchase #7	$110.90	7.132%	$118.8094	$118.81	$118.80	$118.80
7 purchase totals =	$658.57		$705.4938	$705.50	$705.45	$705.40