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	$89.70	12.524%	$100.934	$100.93	$100.95	$100.90
Purchase #2	$37.73	13.652%	$42.8809	$42.88	$42.90	$42.90
Purchase #3	$59.53	7.207%	$63.8203	$63.82	$63.80	$63.80
Purchase #4	$135.60	8.448%	$147.0555	$147.06	$147.05	$147.10
Purchase #5	$88.93	11.145%	$98.8412	$98.84	$98.85	$98.80
Purchase #6	$216.89	8.474%	$235.2693	$235.27	$235.25	$235.30
Purchase #7	$249.69	6.178%	$265.1158	$265.12	$265.10	$265.10
7 purchase totals =	$878.07		$953.9170	$953.92	$953.90	$953.90