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	$22.81	6.582%	$24.3114	$24.31	$24.30	$24.30
Purchase #2	$79.38	13.768%	$90.309	$90.31	$90.30	$90.30
Purchase #3	$6.30	13.165%	$7.1294	$7.13	$7.15	$7.10
Purchase #4	$96.77	12.741%	$109.0995	$109.10	$109.10	$109.10
Purchase #5	$45.33	12.529%	$51.0094	$51.01	$51.00	$51.00
Purchase #6	$39.77	6.321%	$42.2839	$42.28	$42.30	$42.30
Purchase #7	$147.78	9.821%	$162.2935	$162.29	$162.30	$162.30
7 purchase totals =	$438.14		$486.4361	$486.43	$486.45	$486.40