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	$129.40	9.199%	$141.3035	$141.30	$141.30	$141.30
Purchase #2	$54.73	8.315%	$59.2808	$59.28	$59.30	$59.30
Purchase #3	$245.83	11.125%	$273.1786	$273.18	$273.20	$273.20
Purchase #4	$203.32	12.801%	$229.347	$229.35	$229.35	$229.30
Purchase #5	$197.51	4.708%	$206.8088	$206.81	$206.80	$206.80
Purchase #6	$71.27	12.248%	$79.9991	$80.00	$80.00	$80.00
Purchase #7	$81.28	11.489%	$90.6183	$90.62	$90.60	$90.60
7 purchase totals =	$983.34		$1,080.5361	$1,080.54	$1,080.55	$1,080.50