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	$164.93	12.867%	$186.1515	$186.15	$186.15	$186.20
Purchase #2	$25.76	3.805%	$26.7402	$26.74	$26.75	$26.70
Purchase #3	$185.67	11.146%	$206.3648	$206.36	$206.35	$206.40
Purchase #4	$78.45	13.573%	$89.098	$89.10	$89.10	$89.10
Purchase #5	$12.88	3.457%	$13.3253	$13.33	$13.35	$13.30
Purchase #6	$27.89	12.601%	$31.4044	$31.40	$31.40	$31.40
Purchase #7	$250.86	11.765%	$280.3737	$280.37	$280.35	$280.40
7 purchase totals =	$746.44		$833.4579	$833.45	$833.45	$833.50