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	$140.93	4.426%	$147.1676	$147.17	$147.15	$147.20
Purchase #2	$38.77	9.566%	$42.4787	$42.48	$42.50	$42.50
Purchase #3	$71.26	10.489%	$78.7345	$78.73	$78.75	$78.70
Purchase #4	$173.31	7.820%	$186.8628	$186.86	$186.85	$186.90
Purchase #5	$152.70	8.640%	$165.8933	$165.89	$165.90	$165.90
Purchase #6	$113.90	12.588%	$128.2377	$128.24	$128.25	$128.20
Purchase #7	$90.70	5.818%	$95.9769	$95.98	$96.00	$96.00
7 purchase totals =	$781.57		$845.3515	$845.35	$845.40	$845.40