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	$180.76	10.556%	$199.841	$199.84	$199.85	$199.80
Purchase #2	$38.51	12.248%	$43.2267	$43.23	$43.25	$43.20
Purchase #3	$154.64	9.133%	$168.7633	$168.76	$168.75	$168.80
Purchase #4	$197.85	5.828%	$209.3807	$209.38	$209.40	$209.40
Purchase #5	$232.53	13.541%	$264.0169	$264.02	$264.00	$264.00
Purchase #6	$243.56	13.244%	$275.8171	$275.82	$275.80	$275.80
Purchase #7	$87.38	3.383%	$90.3361	$90.34	$90.35	$90.30
7 purchase totals =	$1,135.23		$1,251.3818	$1,251.39	$1,251.40	$1,251.30