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	$30.34	3.331%	$31.3506	$31.35	$31.35	$31.40
Purchase #2	$183.39	4.604%	$191.8333	$191.83	$191.85	$191.80
Purchase #3	$206.27	12.279%	$231.5979	$231.60	$231.60	$231.60
Purchase #4	$162.86	3.582%	$168.6936	$168.69	$168.70	$168.70
Purchase #5	$72.43	7.365%	$77.7645	$77.76	$77.75	$77.80
Purchase #6	$94.47	6.221%	$100.347	$100.35	$100.35	$100.30
Purchase #7	$45.44	4.115%	$47.3099	$47.31	$47.30	$47.30
7 purchase totals =	$795.20		$848.8968	$848.89	$848.90	$848.90