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	$29.82	8.220%	$32.2712	$32.27	$32.25	$32.30
Purchase #2	$249.69	7.867%	$269.3331	$269.33	$269.35	$269.30
Purchase #3	$137.40	12.494%	$154.5668	$154.57	$154.55	$154.60
Purchase #4	$57.63	6.589%	$61.4272	$61.43	$61.45	$61.40
Purchase #5	$24.32	12.860%	$27.4476	$27.45	$27.45	$27.40
Purchase #6	$236.88	12.257%	$265.9144	$265.91	$265.90	$265.90
Purchase #7	$200.35	3.235%	$206.8313	$206.83	$206.85	$206.80
7 purchase totals =	$936.09		$1,017.7916	$1,017.79	$1,017.80	$1,017.70