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	$28.29	11.357%	$31.5029	$31.50	$31.50	$31.50
Purchase #2	$247.91	10.173%	$273.1299	$273.13	$273.15	$273.10
Purchase #3	$34.86	10.760%	$38.6109	$38.61	$38.60	$38.60
Purchase #4	$53.65	13.507%	$60.8965	$60.90	$60.90	$60.90
Purchase #5	$73.96	10.281%	$81.5638	$81.56	$81.55	$81.60
Purchase #6	$160.43	6.789%	$171.3216	$171.32	$171.30	$171.30
Purchase #7	$227.25	8.794%	$247.2344	$247.23	$247.25	$247.20
7 purchase totals =	$826.35		$904.2600	$904.25	$904.25	$904.20