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	$5.29	12.680%	$5.9608	$5.96	$5.95	$6.00
Purchase #2	$150.50	9.853%	$165.3288	$165.33	$165.35	$165.30
Purchase #3	$129.56	8.305%	$140.32	$140.32	$140.30	$140.30
Purchase #4	$52.25	6.577%	$55.6865	$55.69	$55.70	$55.70
Purchase #5	$152.67	6.687%	$162.879	$162.88	$162.90	$162.90
Purchase #6	$63.90	13.122%	$72.285	$72.29	$72.30	$72.30
Purchase #7	$168.37	7.121%	$180.3596	$180.36	$180.35	$180.40
7 purchase totals =	$722.54		$782.8197	$782.83	$782.85	$782.90