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	$81.36	10.643%	$90.0191	$90.02	$90.00	$90.00
Purchase #2	$129.72	10.157%	$142.8957	$142.90	$142.90	$142.90
Purchase #3	$106.63	13.834%	$121.3812	$121.38	$121.40	$121.40
Purchase #4	$175.26	13.641%	$199.1672	$199.17	$199.15	$199.20
Purchase #5	$246.78	10.726%	$273.2496	$273.25	$273.25	$273.20
Purchase #6	$135.27	12.799%	$152.5832	$152.58	$152.60	$152.60
Purchase #7	$137.32	10.674%	$151.9775	$151.98	$152.00	$152.00
7 purchase totals =	$1,012.34		$1,131.2735	$1,131.28	$1,131.30	$1,131.30