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	$96.85	9.242%	$105.8009	$105.80	$105.80	$105.80
Purchase #2	$189.58	10.442%	$209.3759	$209.38	$209.40	$209.40
Purchase #3	$72.42	7.846%	$78.1021	$78.10	$78.10	$78.10
Purchase #4	$141.75	7.490%	$152.3671	$152.37	$152.35	$152.40
Purchase #5	$104.93	9.264%	$114.6507	$114.65	$114.65	$114.70
Purchase #6	$213.88	4.194%	$222.8501	$222.85	$222.85	$222.90
Purchase #7	$98.33	11.588%	$109.7245	$109.72	$109.70	$109.70
7 purchase totals =	$917.74		$992.8713	$992.87	$992.85	$993.00