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	$97.61	6.455%	$103.9107	$103.91	$103.90	$103.90
Purchase #2	$249.33	12.308%	$280.0175	$280.02	$280.00	$280.00
Purchase #3	$82.52	11.365%	$91.8984	$91.90	$91.90	$91.90
Purchase #4	$72.77	12.621%	$81.9543	$81.95	$81.95	$82.00
Purchase #5	$89.76	11.362%	$99.9585	$99.96	$99.95	$100.00
Purchase #6	$43.42	10.649%	$48.0438	$48.04	$48.05	$48.00
Purchase #7	$222.74	6.765%	$237.8084	$237.81	$237.80	$237.80
7 purchase totals =	$858.15		$943.5916	$943.59	$943.55	$943.60