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	$198.91	13.414%	$225.5918	$225.59	$225.60	$225.60
Purchase #2	$38.54	11.739%	$43.0642	$43.06	$43.05	$43.10
Purchase #3	$88.66	12.319%	$99.582	$99.58	$99.60	$99.60
Purchase #4	$224.40	9.181%	$245.0022	$245.00	$245.00	$245.00
Purchase #5	$31.45	12.701%	$35.4445	$35.44	$35.45	$35.40
Purchase #6	$152.46	10.240%	$168.0719	$168.07	$168.05	$168.10
Purchase #7	$214.61	4.294%	$223.8254	$223.83	$223.85	$223.80
7 purchase totals =	$949.03		$1,040.5820	$1,040.57	$1,040.60	$1,040.60