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	$110.91	12.636%	$124.9246	$124.92	$124.90	$124.90
Purchase #2	$162.31	3.764%	$168.4193	$168.42	$168.40	$168.40
Purchase #3	$88.89	11.119%	$98.7737	$98.77	$98.75	$98.80
Purchase #4	$225.32	10.212%	$248.3297	$248.33	$248.35	$248.30
Purchase #5	$77.39	13.204%	$87.6086	$87.61	$87.60	$87.60
Purchase #6	$79.29	3.712%	$82.2332	$82.23	$82.25	$82.20
Purchase #7	$227.61	8.402%	$246.7338	$246.73	$246.75	$246.70
7 purchase totals =	$971.72		$1,057.0229	$1,057.01	$1,057.00	$1,056.90