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	$30.75	5.206%	$32.3508	$32.35	$32.35	$32.40
Purchase #2	$215.99	12.756%	$243.5417	$243.54	$243.55	$243.50
Purchase #3	$237.52	13.830%	$270.369	$270.37	$270.35	$270.40
Purchase #4	$194.29	9.848%	$213.4237	$213.42	$213.40	$213.40
Purchase #5	$64.88	11.605%	$72.4093	$72.41	$72.40	$72.40
Purchase #6	$95.44	12.657%	$107.5198	$107.52	$107.50	$107.50
Purchase #7	$55.88	12.442%	$62.8326	$62.83	$62.85	$62.80
7 purchase totals =	$894.75		$1,002.4469	$1,002.44	$1,002.40	$1,002.40