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	$29.43	12.760%	$33.1853	$33.19	$33.20	$33.20
Purchase #2	$180.57	9.558%	$197.8289	$197.83	$197.85	$197.80
Purchase #3	$81.84	9.695%	$89.7744	$89.77	$89.75	$89.80
Purchase #4	$43.28	5.148%	$45.5081	$45.51	$45.50	$45.50
Purchase #5	$204.33	4.632%	$213.7946	$213.79	$213.80	$213.80
Purchase #6	$248.68	6.606%	$265.1078	$265.11	$265.10	$265.10
Purchase #7	$156.36	5.311%	$164.6643	$164.66	$164.65	$164.70
7 purchase totals =	$944.49		$1,009.8634	$1,009.86	$1,009.85	$1,009.90