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	$222.29	12.242%	$249.5027	$249.50	$249.50	$249.50
Purchase #2	$147.89	6.299%	$157.2056	$157.21	$157.20	$157.20
Purchase #3	$156.37	7.682%	$168.3823	$168.38	$168.40	$168.40
Purchase #4	$209.95	5.804%	$222.1355	$222.14	$222.15	$222.10
Purchase #5	$40.35	4.764%	$42.2723	$42.27	$42.25	$42.30
Purchase #6	$73.51	11.844%	$82.2165	$82.22	$82.20	$82.20
Purchase #7	$159.69	5.724%	$168.8307	$168.83	$168.85	$168.80
7 purchase totals =	$1,010.05		$1,090.5456	$1,090.55	$1,090.55	$1,090.50