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	$35.47	11.108%	$39.41	$39.41	$39.40	$39.40
Purchase #2	$152.53	10.503%	$168.5502	$168.55	$168.55	$168.60
Purchase #3	$208.39	13.322%	$236.1517	$236.15	$236.15	$236.20
Purchase #4	$12.31	6.573%	$13.1191	$13.12	$13.10	$13.10
Purchase #5	$82.90	7.809%	$89.3737	$89.37	$89.35	$89.40
Purchase #6	$191.46	11.560%	$213.5928	$213.59	$213.60	$213.60
Purchase #7	$15.49	5.717%	$16.3756	$16.38	$16.40	$16.40
7 purchase totals =	$698.55		$776.5731	$776.57	$776.55	$776.70