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	$218.26	10.220%	$240.5662	$240.57	$240.55	$240.60
Purchase #2	$141.93	8.816%	$154.4425	$154.44	$154.45	$154.40
Purchase #3	$198.85	12.158%	$223.0262	$223.03	$223.05	$223.00
Purchase #4	$145.49	3.210%	$150.1602	$150.16	$150.15	$150.20
Purchase #5	$68.72	6.394%	$73.114	$73.11	$73.10	$73.10
Purchase #6	$83.93	8.282%	$90.8811	$90.88	$90.90	$90.90
Purchase #7	$31.41	13.718%	$35.7188	$35.72	$35.70	$35.70
7 purchase totals =	$888.59		$967.9090	$967.91	$967.90	$967.90