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	$103.90	5.283%	$109.389	$109.39	$109.40	$109.40
Purchase #2	$125.87	13.266%	$142.5679	$142.57	$142.55	$142.60
Purchase #3	$136.80	11.573%	$152.6319	$152.63	$152.65	$152.60
Purchase #4	$150.92	6.263%	$160.3721	$160.37	$160.35	$160.40
Purchase #5	$84.36	3.760%	$87.5319	$87.53	$87.55	$87.50
Purchase #6	$183.46	11.732%	$204.9835	$204.98	$205.00	$205.00
Purchase #7	$68.50	6.423%	$72.8998	$72.90	$72.90	$72.90
7 purchase totals =	$853.81		$930.3761	$930.37	$930.40	$930.40