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	$81.49	10.582%	$90.1133	$90.11	$90.10	$90.10
Purchase #2	$110.60	12.116%	$124.0003	$124.00	$124.00	$124.00
Purchase #3	$238.90	10.419%	$263.791	$263.79	$263.80	$263.80
Purchase #4	$18.76	10.260%	$20.6848	$20.68	$20.70	$20.70
Purchase #5	$220.72	12.498%	$248.3056	$248.31	$248.30	$248.30
Purchase #6	$245.54	8.190%	$265.6497	$265.65	$265.65	$265.60
Purchase #7	$174.61	12.459%	$196.3647	$196.36	$196.35	$196.40
7 purchase totals =	$1,090.62		$1,208.9094	$1,208.90	$1,208.90	$1,208.90