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	$227.67	10.212%	$250.9197	$250.92	$250.90	$250.90
Purchase #2	$44.86	13.524%	$50.9269	$50.93	$50.95	$50.90
Purchase #3	$179.96	4.405%	$187.8872	$187.89	$187.90	$187.90
Purchase #4	$245.71	7.401%	$263.895	$263.90	$263.90	$263.90
Purchase #5	$75.92	10.122%	$83.6046	$83.60	$83.60	$83.60
Purchase #6	$16.58	8.621%	$18.0094	$18.01	$18.00	$18.00
Purchase #7	$33.90	4.118%	$35.296	$35.30	$35.30	$35.30
7 purchase totals =	$824.60		$890.5388	$890.55	$890.55	$890.50