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	$203.86	6.364%	$216.8337	$216.83	$216.85	$216.80
Purchase #2	$164.61	5.831%	$174.2084	$174.21	$174.20	$174.20
Purchase #3	$150.75	13.546%	$171.1706	$171.17	$171.15	$171.20
Purchase #4	$191.31	11.436%	$213.1882	$213.19	$213.20	$213.20
Purchase #5	$188.78	7.450%	$202.8441	$202.84	$202.85	$202.80
Purchase #6	$42.53	4.229%	$44.3286	$44.33	$44.35	$44.30
Purchase #7	$68.90	13.544%	$78.2318	$78.23	$78.25	$78.20
7 purchase totals =	$1,010.74		$1,100.8054	$1,100.80	$1,100.85	$1,100.70