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	$202.79	10.326%	$223.7301	$223.73	$223.75	$223.70
Purchase #2	$95.40	3.668%	$98.8993	$98.90	$98.90	$98.90
Purchase #3	$178.90	11.228%	$198.9869	$198.99	$199.00	$199.00
Purchase #4	$113.71	6.219%	$120.7816	$120.78	$120.80	$120.80
Purchase #5	$148.89	12.187%	$167.0352	$167.04	$167.05	$167.00
Purchase #6	$31.34	10.265%	$34.5571	$34.56	$34.55	$34.60
Purchase #7	$90.80	9.485%	$99.4124	$99.41	$99.40	$99.40
7 purchase totals =	$861.83		$943.4026	$943.41	$943.45	$943.40