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	$72.54	13.575%	$82.3873	$82.39	$82.40	$82.40
Purchase #2	$109.25	6.639%	$116.5031	$116.50	$116.50	$116.50
Purchase #3	$31.78	10.825%	$35.2202	$35.22	$35.20	$35.20
Purchase #4	$232.73	6.808%	$248.5743	$248.57	$248.55	$248.60
Purchase #5	$14.47	6.539%	$15.4162	$15.42	$15.40	$15.40
Purchase #6	$234.69	11.301%	$261.2123	$261.21	$261.20	$261.20
Purchase #7	$165.59	10.163%	$182.4189	$182.42	$182.40	$182.40
7 purchase totals =	$861.05		$941.7323	$941.73	$941.65	$941.70