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	$39.36	7.453%	$42.2935	$42.29	$42.30	$42.30
Purchase #2	$109.29	9.327%	$119.4835	$119.48	$119.50	$119.50
Purchase #3	$22.57	8.380%	$24.4614	$24.46	$24.45	$24.50
Purchase #4	$135.73	11.168%	$150.8883	$150.89	$150.90	$150.90
Purchase #5	$85.61	3.782%	$88.8478	$88.85	$88.85	$88.80
Purchase #6	$123.68	6.865%	$132.1706	$132.17	$132.15	$132.20
Purchase #7	$95.27	3.570%	$98.6711	$98.67	$98.65	$98.70
7 purchase totals =	$611.51		$656.8162	$656.81	$656.80	$656.90