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	$83.55	11.742%	$93.3604	$93.36	$93.35	$93.40
Purchase #2	$238.78	8.492%	$259.0572	$259.06	$259.05	$259.10
Purchase #3	$47.97	13.294%	$54.3471	$54.35	$54.35	$54.30
Purchase #4	$189.61	10.424%	$209.3749	$209.37	$209.35	$209.40
Purchase #5	$84.30	6.250%	$89.5688	$89.57	$89.55	$89.60
Purchase #6	$96.39	8.173%	$104.268	$104.27	$104.25	$104.30
Purchase #7	$171.54	10.259%	$189.1383	$189.14	$189.15	$189.10
7 purchase totals =	$912.14		$999.1147	$999.12	$999.05	$999.20