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	$168.84	12.270%	$189.5567	$189.56	$189.55	$189.60
Purchase #2	$65.84	11.614%	$73.4867	$73.49	$73.50	$73.50
Purchase #3	$231.58	9.273%	$253.0544	$253.05	$253.05	$253.10
Purchase #4	$36.35	3.786%	$37.7262	$37.73	$37.75	$37.70
Purchase #5	$99.50	9.705%	$109.1565	$109.16	$109.15	$109.20
Purchase #6	$56.88	10.564%	$62.8888	$62.89	$62.90	$62.90
Purchase #7	$165.42	12.581%	$186.2315	$186.23	$186.25	$186.20
7 purchase totals =	$824.41		$912.1008	$912.11	$912.15	$912.20