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	$62.96	6.874%	$67.2879	$67.29	$67.30	$67.30
Purchase #2	$249.33	7.630%	$268.3539	$268.35	$268.35	$268.40
Purchase #3	$108.29	13.822%	$123.2578	$123.26	$123.25	$123.30
Purchase #4	$82.76	8.644%	$89.9138	$89.91	$89.90	$89.90
Purchase #5	$186.75	11.840%	$208.8612	$208.86	$208.85	$208.90
Purchase #6	$171.68	10.355%	$189.4575	$189.46	$189.45	$189.50
Purchase #7	$162.89	3.320%	$168.2979	$168.30	$168.30	$168.30
7 purchase totals =	$1,024.66		$1,115.4300	$1,115.43	$1,115.40	$1,115.60