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	$96.92	3.600%	$100.4091	$100.41	$100.40	$100.40
Purchase #2	$33.96	6.681%	$36.2289	$36.23	$36.25	$36.20
Purchase #3	$207.70	13.306%	$235.3366	$235.34	$235.35	$235.30
Purchase #4	$100.48	4.398%	$104.8991	$104.90	$104.90	$104.90
Purchase #5	$173.29	5.477%	$182.7811	$182.78	$182.80	$182.80
Purchase #6	$149.89	12.669%	$168.8796	$168.88	$168.90	$168.90
Purchase #7	$239.48	11.539%	$267.1136	$267.11	$267.10	$267.10
7 purchase totals =	$1,001.72		$1,095.6480	$1,095.65	$1,095.70	$1,095.60