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	$178.45	6.179%	$189.4764	$189.48	$189.50	$189.50
Purchase #2	$233.72	3.501%	$241.9025	$241.90	$241.90	$241.90
Purchase #3	$204.40	5.564%	$215.7728	$215.77	$215.75	$215.80
Purchase #4	$136.95	7.741%	$147.5513	$147.55	$147.55	$147.60
Purchase #5	$237.69	11.853%	$265.8634	$265.86	$265.85	$265.90
Purchase #6	$144.34	12.460%	$162.3248	$162.32	$162.30	$162.30
Purchase #7	$190.98	3.740%	$198.1227	$198.12	$198.10	$198.10
7 purchase totals =	$1,326.53		$1,421.0139	$1,421.00	$1,420.95	$1,421.10