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	$23.34	6.556%	$24.8702	$24.87	$24.85	$24.90
Purchase #2	$186.81	6.147%	$198.2932	$198.29	$198.30	$198.30
Purchase #3	$81.70	7.134%	$87.5285	$87.53	$87.55	$87.50
Purchase #4	$96.93	13.288%	$109.8101	$109.81	$109.80	$109.80
Purchase #5	$42.70	6.581%	$45.5101	$45.51	$45.50	$45.50
Purchase #6	$80.57	12.698%	$90.8008	$90.80	$90.80	$90.80
Purchase #7	$190.28	3.220%	$196.407	$196.41	$196.40	$196.40
7 purchase totals =	$702.33		$753.2199	$753.22	$753.20	$753.20