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	$35.97	7.836%	$38.7886	$38.79	$38.80	$38.80
Purchase #2	$232.42	11.232%	$258.5254	$258.53	$258.55	$258.50
Purchase #3	$193.48	11.347%	$215.4342	$215.43	$215.45	$215.40
Purchase #4	$78.30	4.869%	$82.1124	$82.11	$82.10	$82.10
Purchase #5	$169.34	4.114%	$176.3066	$176.31	$176.30	$176.30
Purchase #6	$127.45	11.107%	$141.6059	$141.61	$141.60	$141.60
Purchase #7	$86.77	12.424%	$97.5503	$97.55	$97.55	$97.60
7 purchase totals =	$923.73		$1,010.3234	$1,010.33	$1,010.35	$1,010.30