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	$157.42	9.198%	$171.8995	$171.90	$171.90	$171.90
Purchase #2	$62.96	13.404%	$71.3992	$71.40	$71.40	$71.40
Purchase #3	$236.43	3.568%	$244.8658	$244.87	$244.85	$244.90
Purchase #4	$91.90	6.360%	$97.7448	$97.74	$97.75	$97.70
Purchase #5	$202.90	5.140%	$213.3291	$213.33	$213.35	$213.30
Purchase #6	$64.30	4.316%	$67.0752	$67.08	$67.10	$67.10
Purchase #7	$109.47	7.400%	$117.5708	$117.57	$117.55	$117.60
7 purchase totals =	$925.38		$983.8844	$983.89	$983.90	$983.90