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	$142.33	3.514%	$147.3315	$147.33	$147.35	$147.30
Purchase #2	$82.75	9.372%	$90.5053	$90.51	$90.50	$90.50
Purchase #3	$81.66	9.867%	$89.7174	$89.72	$89.70	$89.70
Purchase #4	$237.45	3.334%	$245.3666	$245.37	$245.35	$245.40
Purchase #5	$146.48	8.392%	$158.7726	$158.77	$158.75	$158.80
Purchase #6	$73.55	7.639%	$79.1685	$79.17	$79.15	$79.20
Purchase #7	$113.85	13.199%	$128.8771	$128.88	$128.90	$128.90
7 purchase totals =	$878.07		$939.7390	$939.75	$939.70	$939.80