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	$117.43	11.787%	$131.2715	$131.27	$131.25	$131.30
Purchase #2	$240.77	12.469%	$270.7916	$270.79	$270.80	$270.80
Purchase #3	$250.84	12.459%	$282.0922	$282.09	$282.10	$282.10
Purchase #4	$112.40	13.435%	$127.5009	$127.50	$127.50	$127.50
Purchase #5	$83.69	11.721%	$93.4993	$93.50	$93.50	$93.50
Purchase #6	$22.40	9.108%	$24.4402	$24.44	$24.45	$24.40
Purchase #7	$161.35	12.104%	$180.8798	$180.88	$180.90	$180.90
7 purchase totals =	$988.88		$1,110.4755	$1,110.47	$1,110.50	$1,110.50