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	$36.46	9.523%	$39.9321	$39.93	$39.95	$39.90
Purchase #2	$150.34	13.478%	$170.6028	$170.60	$170.60	$170.60
Purchase #3	$54.46	4.842%	$57.097	$57.10	$57.10	$57.10
Purchase #4	$196.85	4.805%	$206.3086	$206.31	$206.30	$206.30
Purchase #5	$247.90	13.261%	$280.774	$280.77	$280.75	$280.80
Purchase #6	$213.27	4.614%	$223.1103	$223.11	$223.10	$223.10
Purchase #7	$250.35	4.292%	$261.095	$261.10	$261.10	$261.10
7 purchase totals =	$1,149.63		$1,238.9198	$1,238.92	$1,238.90	$1,238.90