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	$83.67	7.385%	$89.849	$89.85	$89.85	$89.80
Purchase #2	$128.49	6.692%	$137.0886	$137.09	$137.10	$137.10
Purchase #3	$65.27	6.440%	$69.4734	$69.47	$69.45	$69.50
Purchase #4	$104.96	9.393%	$114.8189	$114.82	$114.80	$114.80
Purchase #5	$117.98	13.533%	$133.9462	$133.95	$133.95	$133.90
Purchase #6	$28.86	3.648%	$29.9128	$29.91	$29.90	$29.90
Purchase #7	$86.46	11.416%	$96.3303	$96.33	$96.35	$96.30
7 purchase totals =	$615.69		$671.4192	$671.42	$671.40	$671.30