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	$43.86	8.371%	$47.5315	$47.53	$47.55	$47.50
Purchase #2	$94.28	5.850%	$99.7954	$99.80	$99.80	$99.80
Purchase #3	$248.89	13.497%	$282.4827	$282.48	$282.50	$282.50
Purchase #4	$228.80	9.252%	$249.9686	$249.97	$249.95	$250.00
Purchase #5	$46.97	13.253%	$53.1949	$53.19	$53.20	$53.20
Purchase #6	$165.77	3.630%	$171.7875	$171.79	$171.80	$171.80
Purchase #7	$89.69	11.419%	$99.9317	$99.93	$99.95	$99.90
7 purchase totals =	$918.26		$1,004.6923	$1,004.69	$1,004.75	$1,004.70