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	$88.27	13.638%	$100.3083	$100.31	$100.30	$100.30
Purchase #2	$250.98	6.835%	$268.1345	$268.13	$268.15	$268.10
Purchase #3	$242.52	11.651%	$270.776	$270.78	$270.80	$270.80
Purchase #4	$28.96	10.122%	$31.8913	$31.89	$31.90	$31.90
Purchase #5	$237.88	5.218%	$250.2926	$250.29	$250.30	$250.30
Purchase #6	$224.56	4.704%	$235.1233	$235.12	$235.10	$235.10
Purchase #7	$210.55	8.873%	$229.2321	$229.23	$229.25	$229.20
7 purchase totals =	$1,283.72		$1,385.7581	$1,385.75	$1,385.80	$1,385.70