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	$25.32	11.791%	$28.3055	$28.31	$28.30	$28.30
Purchase #2	$152.46	4.213%	$158.8831	$158.88	$158.90	$158.90
Purchase #3	$185.36	6.826%	$198.0127	$198.01	$198.00	$198.00
Purchase #4	$125.70	3.249%	$129.784	$129.78	$129.80	$129.80
Purchase #5	$219.61	13.804%	$249.925	$249.93	$249.95	$249.90
Purchase #6	$140.51	7.394%	$150.8993	$150.90	$150.90	$150.90
Purchase #7	$198.76	8.615%	$215.8832	$215.88	$215.90	$215.90
7 purchase totals =	$1,047.72		$1,131.6928	$1,131.69	$1,131.75	$1,131.70