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	$80.70	9.489%	$88.3576	$88.36	$88.35	$88.40
Purchase #2	$93.96	5.576%	$99.1992	$99.20	$99.20	$99.20
Purchase #3	$137.35	8.440%	$148.9423	$148.94	$148.95	$148.90
Purchase #4	$165.59	5.432%	$174.5848	$174.58	$174.60	$174.60
Purchase #5	$133.37	10.205%	$146.9804	$146.98	$147.00	$147.00
Purchase #6	$213.80	4.352%	$223.1046	$223.10	$223.10	$223.10
Purchase #7	$130.69	6.660%	$139.394	$139.39	$139.40	$139.40
7 purchase totals =	$955.46		$1,020.5629	$1,020.55	$1,020.60	$1,020.60