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	$33.80	8.155%	$36.5564	$36.56	$36.55	$36.60
Purchase #2	$168.89	6.407%	$179.7108	$179.71	$179.70	$179.70
Purchase #3	$197.69	6.670%	$210.8759	$210.88	$210.90	$210.90
Purchase #4	$184.46	7.636%	$198.5454	$198.55	$198.55	$198.50
Purchase #5	$131.70	11.695%	$147.1023	$147.10	$147.10	$147.10
Purchase #6	$162.50	12.370%	$182.6013	$182.60	$182.60	$182.60
Purchase #7	$125.56	9.846%	$137.9226	$137.92	$137.90	$137.90
7 purchase totals =	$1,004.60		$1,093.3147	$1,093.32	$1,093.30	$1,093.30