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	$94.29	5.871%	$99.8258	$99.83	$99.85	$99.80
Purchase #2	$82.88	12.650%	$93.3643	$93.36	$93.35	$93.40
Purchase #3	$248.96	10.510%	$275.1257	$275.13	$275.15	$275.10
Purchase #4	$187.39	3.532%	$194.0086	$194.01	$194.00	$194.00
Purchase #5	$66.63	7.861%	$71.8678	$71.87	$71.85	$71.90
Purchase #6	$192.90	4.595%	$201.7638	$201.76	$201.75	$201.80
Purchase #7	$189.71	11.160%	$210.8816	$210.88	$210.90	$210.90
7 purchase totals =	$1,062.76		$1,146.8376	$1,146.84	$1,146.85	$1,146.90