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	$105.77	3.582%	$109.5587	$109.56	$109.55	$109.60
Purchase #2	$180.73	10.228%	$199.2151	$199.22	$199.20	$199.20
Purchase #3	$80.39	11.439%	$89.5858	$89.59	$89.60	$89.60
Purchase #4	$88.53	3.783%	$91.8791	$91.88	$91.90	$91.90
Purchase #5	$96.95	5.545%	$102.3259	$102.33	$102.35	$102.30
Purchase #6	$184.62	11.349%	$205.5725	$205.57	$205.55	$205.60
Purchase #7	$17.69	5.115%	$18.5948	$18.59	$18.60	$18.60
7 purchase totals =	$754.68		$816.7319	$816.74	$816.75	$816.80