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	$77.98	5.755%	$82.4677	$82.47	$82.45	$82.50
Purchase #2	$157.44	9.220%	$171.956	$171.96	$171.95	$172.00
Purchase #3	$141.29	4.223%	$147.2567	$147.26	$147.25	$147.30
Purchase #4	$208.33	3.817%	$216.282	$216.28	$216.30	$216.30
Purchase #5	$5.41	10.497%	$5.9779	$5.98	$6.00	$6.00
Purchase #6	$171.48	11.285%	$190.8315	$190.83	$190.85	$190.80
Purchase #7	$238.94	11.108%	$265.4815	$265.48	$265.50	$265.50
7 purchase totals =	$1,000.87		$1,080.2533	$1,080.26	$1,080.30	$1,080.40