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	$181.36	4.104%	$188.803	$188.80	$188.80	$188.80
Purchase #2	$144.39	11.417%	$160.875	$160.88	$160.90	$160.90
Purchase #3	$193.98	6.240%	$206.0844	$206.08	$206.10	$206.10
Purchase #4	$57.37	4.417%	$59.904	$59.90	$59.90	$59.90
Purchase #5	$84.73	5.840%	$89.6782	$89.68	$89.70	$89.70
Purchase #6	$245.79	9.868%	$270.0446	$270.04	$270.05	$270.00
Purchase #7	$181.93	4.257%	$189.6748	$189.67	$189.65	$189.70
7 purchase totals =	$1,089.55		$1,165.0640	$1,165.05	$1,165.10	$1,165.10