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	$131.51	11.851%	$147.0953	$147.10	$147.10	$147.10
Purchase #2	$84.62	6.228%	$89.8901	$89.89	$89.90	$89.90
Purchase #3	$162.97	7.293%	$174.8554	$174.86	$174.85	$174.90
Purchase #4	$77.78	13.763%	$88.4849	$88.48	$88.50	$88.50
Purchase #5	$108.40	4.229%	$112.9842	$112.98	$113.00	$113.00
Purchase #6	$26.54	7.483%	$28.526	$28.53	$28.55	$28.50
Purchase #7	$178.37	7.303%	$191.3964	$191.40	$191.40	$191.40
7 purchase totals =	$770.19		$833.2323	$833.24	$833.30	$833.30