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	$28.69	10.815%	$31.7928	$31.79	$31.80	$31.80
Purchase #2	$199.39	3.402%	$206.1732	$206.17	$206.15	$206.20
Purchase #3	$134.39	13.419%	$152.4238	$152.42	$152.40	$152.40
Purchase #4	$245.47	7.616%	$264.165	$264.17	$264.15	$264.20
Purchase #5	$82.54	8.564%	$89.6087	$89.61	$89.60	$89.60
Purchase #6	$41.93	5.143%	$44.0865	$44.09	$44.10	$44.10
Purchase #7	$136.79	9.809%	$150.2077	$150.21	$150.20	$150.20
7 purchase totals =	$869.20		$938.4577	$938.46	$938.40	$938.50