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	$75.47	9.669%	$82.7672	$82.77	$82.75	$82.80
Purchase #2	$44.30	3.185%	$45.711	$45.71	$45.70	$45.70
Purchase #3	$68.75	13.522%	$78.0464	$78.05	$78.05	$78.00
Purchase #4	$178.30	12.754%	$201.0404	$201.04	$201.05	$201.00
Purchase #5	$129.47	5.717%	$136.8718	$136.87	$136.85	$136.90
Purchase #6	$78.73	4.740%	$82.4618	$82.46	$82.45	$82.50
Purchase #7	$55.90	12.817%	$63.0647	$63.06	$63.05	$63.10
7 purchase totals =	$630.92		$689.9633	$689.96	$689.90	$690.00