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	$81.57	10.474%	$90.1136	$90.11	$90.10	$90.10
Purchase #2	$149.52	10.282%	$164.8936	$164.89	$164.90	$164.90
Purchase #3	$213.97	12.279%	$240.2434	$240.24	$240.25	$240.20
Purchase #4	$182.83	7.386%	$196.3338	$196.33	$196.35	$196.30
Purchase #5	$27.97	5.343%	$29.4644	$29.46	$29.45	$29.50
Purchase #6	$140.45	6.134%	$149.0652	$149.07	$149.05	$149.10
Purchase #7	$47.56	3.651%	$49.2964	$49.30	$49.30	$49.30
7 purchase totals =	$843.87		$919.4104	$919.40	$919.40	$919.40