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	$81.36	9.222%	$88.863	$88.86	$88.85	$88.90
Purchase #2	$18.97	6.860%	$20.2713	$20.27	$20.25	$20.30
Purchase #3	$246.62	3.333%	$254.8398	$254.84	$254.85	$254.80
Purchase #4	$40.57	3.526%	$42.0005	$42.00	$42.00	$42.00
Purchase #5	$172.56	7.142%	$184.8842	$184.88	$184.90	$184.90
Purchase #6	$141.69	7.436%	$152.2261	$152.23	$152.25	$152.20
Purchase #7	$147.67	13.272%	$167.2688	$167.27	$167.25	$167.30
7 purchase totals =	$849.44		$910.3537	$910.35	$910.35	$910.40