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	$167.72	9.713%	$184.0106	$184.01	$184.00	$184.00
Purchase #2	$24.98	13.724%	$28.4083	$28.41	$28.40	$28.40
Purchase #3	$83.91	7.298%	$90.0338	$90.03	$90.05	$90.00
Purchase #4	$152.54	8.519%	$165.5349	$165.53	$165.55	$165.50
Purchase #5	$9.78	12.662%	$11.0183	$11.02	$11.00	$11.00
Purchase #6	$125.70	9.327%	$137.424	$137.42	$137.40	$137.40
Purchase #7	$199.25	11.234%	$221.6337	$221.63	$221.65	$221.60
7 purchase totals =	$763.88		$838.0636	$838.05	$838.05	$837.90