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	$7.40	3.602%	$7.6665	$7.67	$7.65	$7.70
Purchase #2	$238.39	3.330%	$246.3284	$246.33	$246.35	$246.30
Purchase #3	$188.46	4.153%	$196.2867	$196.29	$196.30	$196.30
Purchase #4	$162.66	3.611%	$168.5337	$168.53	$168.55	$168.50
Purchase #5	$79.69	11.132%	$88.5611	$88.56	$88.55	$88.60
Purchase #6	$89.54	10.824%	$99.2318	$99.23	$99.25	$99.20
Purchase #7	$106.48	4.820%	$111.6123	$111.61	$111.60	$111.60
7 purchase totals =	$872.62		$918.2205	$918.22	$918.25	$918.20