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	$76.86	10.190%	$84.692	$84.69	$84.70	$84.70
Purchase #2	$153.42	7.585%	$165.0569	$165.06	$165.05	$165.10
Purchase #3	$88.41	7.350%	$94.9081	$94.91	$94.90	$94.90
Purchase #4	$31.95	13.830%	$36.3687	$36.37	$36.35	$36.40
Purchase #5	$124.47	5.675%	$131.5337	$131.53	$131.55	$131.50
Purchase #6	$54.33	13.122%	$61.4592	$61.46	$61.45	$61.50
Purchase #7	$81.94	13.347%	$92.8765	$92.88	$92.90	$92.90
7 purchase totals =	$611.38		$666.8951	$666.90	$666.90	$667.00